Lesson Plans: Grades 9-12

The Korean War: “Police Action,” 1950–1953


The Lesson


U.S. troops storming the beach at Inchon, South Korea, September 15, 1950.

U.S. troops storming the beach at Inchon, South Korea, September 15, 1950.

Credit: Image courtesy of American Memory at the Library of Congress.

In Europe, East and West eyed each other anxiously across the Iron Curtain. In Asia, the Cold War grew hot. In 1950, North Korean forces, armed mainly with Soviet weapons, invaded South Korea in an effort to reunite the peninsula under communist rule. Within the next couple of days the Truman administration and the United Nations had decided to aid in the defense of South Korea, and soon a multinational army had arrived under the command of General Douglas MacArthur. But while MacArthur was able to prevent the North Koreans from overrunning the South, an unexpected intervention by China soon turned the "police action" (as Truman called it) into a bloody stalemate. Differences between Truman and MacArthur led to the latter's firing in early 1951, and as the war ground on it grew more and more unpopular in the United States. Ultimately it would contribute to Dwight Eisenhower's election as president in 1952, and it would be the Eisenhower administration that brought an end to the conflict through a compromise peace.

This lesson will introduce students to the conflict by having them read the most important administration documents related to it. Specifically it will address four major issues: 1) Truman's decision to send troops to Korea; 2) The decision to cross the 38th Parallel into North Korea, at the risk of a wider war with China; 3) Truman's decision to fire MacArthur; and 4) the war's growing unpopularity in the United States.

Guiding Questions

  • Did the war in Korea represent a triumph or a failure of American foreign policy?

Learning Objectives

After completing this lesson, students should be able to

  • Explain why the United States became involved in the war in Korea
  • Assess the decision to send U.S. and UN forces across the 38th Parallel into North Korea
  • Discuss the conflict between Truman and MacArthur, culminating in the latter's dismissal from command
  • Articulate the reasons why the war became unpopular in the United States
  • Identify on a world map foreign countries associated with the Korean War
  • Identify key terms and individuals associated with the Korean War


Truman's decision to intervene in the Korean War represents a serious departure from previous U.S. foreign policy; after all, the notion that the country had a vital stake in the outcome of a war on the Asian mainland would never have been taken seriously before World War II. That the president acted as he did—and Americans (at least initially) supported that decision—reflects a new understanding of the role of the United States in world affairs. In 1947 the administration committed the country to a policy of "containment," in which communism would be allowed to remain where it already existed, but the Soviet Union and its allies would not be allowed to gain control of any new areas deemed important to America's national security. But there was a moral dimension to this as well, which the president put forward in the so-called "Truman Doctrine" speech of 1947. In that speech Truman committed the country—at least on paper—to the defense of "free peoples" everywhere against communist aggression. Korea would be the first place where American troops would fight and die for that principle. (Containment and the Truman Doctrine are covered in the EDSITEment lesson plan "The Strategy of Containment," lesson #2 in the curriculum unit entitled "Origins of the Cold War".

Ever since the late 19th century Korea had been under Japanese rule, but was liberated by U.S. and Soviet troops in 1945. To avoid conflict between the two wartime allies, they agreed to a temporary division of the country along the 38th Parallel—with Soviet forces in the North, and American troops occupying the South.

With the encouragement of the United States the South held elections in the spring of 1948. The Soviets objected, claiming that the country should continue to be ruled by the occupying armies until a government could be established for the entire country. They instructed their supporters in South Korea to boycott the election, and the result was a resounding victory for Syngman Rhee, a dedicated anti-Communist who had been educated in the United States. In retaliation the Soviets announced the formation of a communist government in North Korea, under the leadership of Kim Il-Sung. By the middle of 1949 both halves of Korea had been recognized as independent countries, and all U.S. and Soviet troops had been withdrawn from the Korean peninsula.

Meanwhile, events in China dealt a serious blow to the containment strategy. Since the early 1930s China had been torn by civil war between the ruling Nationalist Party of Chiang Kai-shek and a communist insurgency under the leadership of Mao Tse-tung. This struggle had died down somewhat during World War II, as both sides temporarily concentrated on the greater threat of Japanese imperialism. However, after the defeat of Japan the civil war resumed. The United States during the war had committed itself to the Nationalists, but by 1948 State Department officials who visited the country had concluded that Chiang's regime was too corrupt and unpopular to survive, and advised Truman to cut off aid. Truman rejected this advice, but the continuation of aid was not enough to save the Nationalists. On October 1, 1949, Mao Tse-tung declared China a "People's Republic," and two months later Chiang Kai-shek and his followers fled to Taiwan, where they set up a government of their own.

The triumph of communism in China would have important implications for the Korean situation. Neither the North nor the South was happy with the division of the country. Kim Il-Sung repeatedly asked Stalin for permission to launch an invasion of the South, and finally convinced him that the United States would not intervene in any Korean conflict. According to recently released archival documents, Stalin agreed to allow a North Korean attack, but warned Kim that while the Soviet Union would continue to provide military and economic aid to the North, the country would not become directly involved.

The North Korean invasion began on June 25, 1950, and it quickly became apparent that South Korea's armed forces were not up to the task of defending their country. President Truman authorized the use of the U.S. military to protect civilians as they retreated before the enemy advance. However, after the United Nations called upon its members to help South Korea resist (the resolution only managed to win approval from the U.N. Security Council because the Soviet delegation was boycotting its proceedings at the time), Truman ordered General Douglas MacArthur—hero of the Pacific Theater in World War II—to take command of a multinational force to assist in the defense of South Korea.

The arrival of United Nations forces—and a spectacular surprise invasion at Inchon, behind the North Korean lines—brought an end to the communist advance in mid-September, but this led to a fundamental reevaluation of the war's purpose. The North Koreans simply began to withdraw toward their own borders, so what had once been simply an effort to defend South Korea now became an effort to punish the North. Although some in the Truman administration became concerned that this might lead to intervention on the part of China, Korea's communist neighbor to the North, the president authorized MacArthur to lead his forces across the 38th Parallel. If the Chinese did intervene, MacArthur assured, their army would quickly be crushed.

MacArthur was wrong—in late October 1950 the Chinese sent a massive army across the Yalu River into North Korea, and the forces of the United Nations immediately fell back. After several weeks of heavy fighting the battle lines finally stabilized—not too far away from the 38th Parallel—and there they would remain for the duration of the conflict.

Most Americans in 1950 would have looked back upon the Second World War as a model of how wars were supposed to take place. The country would be expected to engage in an all-out effort against the enemy, leading to a resounding victory and, probably, the unconditional surrender of the foe. But things would be different this time. Truman wanted to avoid turning the Korean conflict into an all-out war against the Soviet Union and its allies, with the real risk that nuclear weapons might be used. His strategy of "limited war," however, came into conflict with that of General MacArthur, who repeatedly called for the bombing of China, a blockade of the Chinese coast, and the "unleashing" of anti-communist Chinese forces from Taiwan. The tension between the two men—particularly MacArthur's tendency to publicize his criticism of administration policy—led to the general's firing early in 1951.

"Limited war," however, was not only unpopular with MacArthur-most Americans were uncomfortable with it as well. As the conflict grew into a stalemate, the popularity of Truman's decision to intervene plummeted. The Republican Party, which hadn't seen one of its own elected president since 1928, made Korea the centerpiece of their campaign for the White House in 1952. The party's candidate in that year, Dwight D. Eisenhower, pledged that if elected he would go to Korea personally in an effort to bring an end to the fighting. He kept this promise while still President-elect, and an armistice was finally concluded in July 1953.

For teachers seeking additional information about the Korean War, an excellent resource is "The Korean War and its Origins," a site sponsored jointly by the Truman Presidential Library. In addition to an outstanding collection of documents (some of which are used in this lesson), the site includes oral histories, photographs, and a detailed chronology of the war.

Preparation Instructions

Review the lesson plan. Locate and bookmark suggested materials and links from EDSITEment-reviewed websites used in this lesson. Download and print out selected documents and duplicate copies as necessary for student viewing. Alternatively, excerpted versions of these documents are available as part of the downloadable Text Document.

Download the Text Document for this lesson, available here as a PDF. This file contains excerpted versions of the documents used in this lesson, as well as questions for students to answer. Print out and make an appropriate number of copies of the handouts you plan to use in class.

Analyzing primary sources

If your students lack experience in dealing with primary sources, you might use one or more preliminary exercises to help them develop these skills. The Learning Page at the American Memory Project of the Library of Congress includes a set of such activities. Another useful resource is the Digital Classroom of the National Archives, which features a set of Document Analysis Worksheets. Finally, History Matters offers helpful pages on "Making Sense of Documentary Photography" and "Making Sense of Maps" which give helpful advice to teachers in getting their students to use such sources effectively.

Lesson Activities

Activity 1. Public Opinion and the Korean War

Finally, the fourth activity will address the war's unpopularity at home. Students will look at the results of public opinion polls taken in late 1952 and early 1953, excerpts from Eisenhower's famous "I will go to Korea" campaign speech, a letter sent to Truman from the father of a young man killed in the conflict, and a map illustrating how the war had resulted in stalemate by the end of 1951. All of these resources may be found on the sites of the Truman and Eisenhower libraries. Links, and abridged versions of these sources, are available on pages 21–24 of the Text Document.

Ask the students to draw on these documents, in addition to what they have already learned about the Korean War, to write a brief essay in response to the following question: "What did the American public think about the war by late 1952 – early 1953? What factors do you think influenced their opinions?"

Each essay should consist of at least three paragraphs. Each paragraph should include a general statement and at least two sentences citing facts from the documents to back up their generalizations.

Activity 2. Truman vs. MacArthur

In the third activity students will be introduced to the conflict between President Truman and General MacArthur, which culminated in the General's dismissal from command in April 1951. Begin by playing for students the following radio news bulletin (linked from Teaching American History) announcing that MacArthur has been fired (it is quite brief—37 seconds).

Next present them with background information about the stormy relationship between the two men. They should begin by returning to the interactive timeline, and under "East Asia" and "1950" click on "Meeting on Wake Island between Truman and MacArthur" and "Chinese Troops Enter North Korea" and reading the text that appears. Then under "1951" they should click on "Truman Dismisses MacArthur from Command" and do the same. As with above, if students do not have computer access, the teacher could either project the timeline on the board or distribute copies of the timeline included on pages 14–15 of the Text Document. Discuss with students the nature and consequences of the relationship between these two powerful men.

Then have the class simulate a congressional hearing to determine whether Truman's decision to fire MacArthur was justified. Select two students from the class, one to portray Truman and the other MacArthur. The students portraying Truman and MacArthur should read the following documents in preparation (excerpted on pages 16–18 of the Text Document):

The rest of the class should be divided into two groups, those favoring Truman (Democrats) and those favoring MacArthur (Republicans). Regardless of which group they are in, they should be instructed to read the following documents (excerpted on pages 19–20 of the Text Document):

After the students have completed their readings (this could usefully be assigned as homework) the hearings can begin. Have the students portraying Truman and MacArthur each give a brief (five minutes should suffice) presentation laying out their case. Then open the floor to questioning by the class. First a student from the Democratic side should ask a question, then one from the Republican side, and so on until there are no more questions. Students should develop these questions the night before as homework. Some suggestions might be:

"Mr. President, why do you oppose General MacArthur's proposal to use Nationalist Chinese troops from Taiwan?"

"General MacArthur, why did you defy the President's order by making public statements about Korea without first getting approval from the White House?"

Finally, at the end of the exercise ask the students whether or not they believe Truman was right to fire MacArthur.

Activity 3. The Decision to Cross the 38th Parallel

In this activity students will read documents pertaining to the decision to cross the 38th Parallel and enter North Korea; i.e., the decision to change the object of war from the defense of South Korea to the punishment of North Korea.

First, students should read about the landing at Inchon, which threw North Korean forces on the defensive and ultimately pushed them back into their own country. They can do this by visiting the interactive timeline and in the "East Asia" section under 1950 click on the line that says "U.S. Forces Land at Inchon." After they read this they should consult a map of Korea in October 1950, which shows the progress of United Nations forces in the weeks following Inchon. Once again, if students do not have access to computers, this should be projected onto the board for students to see. Regardless of the method used, teacher should spend 10–15 minutes orally reviewing the information from the timeline with the students. A timeline of developments in the war is also available on pages 8–9 of the PDF Text Document.

Once students have familiarized themselves with the overall military situation—that is, the rapid advance of UN forces and the retreat of the North Korean Army—they should read excerpts from the following documents, available at the Truman Presidential Library and Teaching American History. Excerpts are available on pages 10–12 of the Text Document. As they do so, they should complete the worksheet located on page 13, listing both the reasons for crossing the 38th Parallel, and for not doing so.

Depending on how much class time is available, these documents could either be read individually or orally as a group. After students have finished reading the documents and completing the chart, which could take about 30 minutes, have students pair off and go over their chart with a partner. Students should create a group list that will be shared with the entire class. As a large group, place all of the reasons for and against crossing the 38th parallel on the board. To conclude, hold an in-class discussion, asking the students what they would do in this situation if they were president. They should be cautioned to think in terms of the world of the 1950s, rather than today's world. Afterward, explain to them that Truman ultimately decided to authorize MacArthur to cross the 38th Parallel and invade North Korea.

To save on class time (this activity will require approximately 60 minutes), one could assign the documents for homework and use class time for the group work and class discussion.

Activity 4. The Decision to Intervene in Korea

Students should have at least a basic understanding of America's Cold War foreign policy before tackling this lesson. If they have not done lesson #2—"The Strategy of Containment" in the EDSITEment curriculum unit "The Origins of the Cold War"—they should at least have a working definition of "containment" before you begin this lesson. Present them with the following quote, from George Kennan's influential article "The Sources of Soviet Conduct," which appeared in the July 1947 issue of Foreign Affairs:

... [I]t is clear that the main element of any United States policy toward the Soviet Union must be that of long-term, patient but firm and vigilant containment of Russian expansive tendencies.

It might also be helpful to read to them the following passage from the 1947 Truman Doctrine speech:

I believe that it must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures. I believe that we must assist free peoples to work out their own destinies in their own way.

Ask students what they think is the meaning of the two statements. Explain to them that while Truman and his administration believed that it was impossible to eliminate communism where it already existed (in 1947 that basically meant the Soviet Union and Eastern Europe), they also believed the United States could and should act to prevent communism from spreading to other parts of the world.

In the first activity students will examine Truman's decision to commit U.S. forces to Korea. To begin, students should consult this interactive timeline. Ask students to click on "East Asia" in the upper-right-hand corner, and then click on "1945" along the left-hand side of the screen. Next to the date "August 10, 1945" is the headline "Korea Divided along 38th Parallel." Have students click on that and read the text. Continue by asking them to click on the years 1946, 1948, 1949, and 1950 and read about the hyperlinked events up to and including June 25, 1950—the day North Korean forces invaded South Korea. This should provide them with sufficient background on how the war began. If teachers do not have access to the computer lab for this introduction, teachers should project the timeline onto the board and orally go over the events leading up to the Korean War. In addition, a timeline tracing the events leading up to Truman's decision to commit troops to Korea is available on pages 1–3 of the Text Document that accompanies this lesson. Teachers may wish to photocopy and distribute this timeline to the students and go through it with them in class.

After going over the key events leading up to the Korean War, teachers should read aloud the following telegram by President Harry S. Truman (available at the site of the Truman Library, accessible via History Matters, or in excerpted form on page 4 of the Text Document that accompanies this lesson):

Direct students to the following map, available at the site of the U.S. Military Academy at West Point (linked from the EDSITEment-reviewed site History Matters):

Using this map (which could be projected on a screen in the classroom, printed, copied, and distributed to the class, or if computers are available, students might be directed to it online), point out the locations described in the document with the students.

Finally, students will read a series of documents—for homework—from the EDSITEment-reviewed sites Teaching American History and the Truman Presidential Library concerning the president's decision to commit U.S. forces to Korea. The following documents will be used in this activity; links to all of them and excerpted versions of the longer ones, are available on pages 5–7 of the PDF Text Document that accompanies this lesson.

Using the above readings, plus what they have already learned in class about the origins and outbreak of the Korean War, students should then be instructed to write as homework a three-paragraph letter to the editor in which they defend Truman's decision to commit U.S. forces to the defense of South Korea. Each paragraph should consist of a general statement as well as at least two facts, drawn from the documents, to back up that statement.


After completing this lesson, students should be able to write brief (1–2 paragraph) essays answering the following questions:

  • What factors influenced Truman's decision to commit U.S. forces to the defense of South Korea?
  • Analyze the significance of Truman's decision to allow MacArthur to cross the 38th Parallel. Why was this decision important?
  • Why did Truman fire MacArthur? Do you believe that this decision was justified?
  • What factors made the war in Korea so unpopular by 1952?

For advanced students it may be possible to collapse these questions into a single larger question: Did the war in Korea represent a triumph or a failure of American foreign policy?

Students should be able to identify and explain the significance of the following:

  • Douglas MacArthur
  • Inchon
  • 38th Parallel
  • Wake Island Conference

On a blank map of East Asia students should be able to identify the following locations:

  • North Korea
  • South Korea
  • China
  • Taiwan

Extending The Lesson

Teachers who have additional time to devote to the Korean War might consider showing a movie set in or about the war. Some possibilities include: The Bridges at Toko-ri (1954), Pork Chop Hill (1959), or Tae Guk Gi: The Brotherhood of War (2004, a South Korean film, but available with subtitles).

Teachers who want to pay more attention to combat conditions in Korea may want to direct students to the Rutgers Oral History Archives (accessible via the EDSITEment-reviewed resource History Matters), which includes the reminiscences of a wide variety of men who fought there.

Teachers might also wish to have students construct a timeline of the events surrounding the Korean War. An online template for this is available at "Read-Write-Think." An excellent source of information to help students fill in the gaps is "The Korean War and its Origins," a site sponsored by the Truman Presidential Library.

Selected EDSITEment Websites

The Basics

Grade Level


Time Required

3-4 class periods

Subject Areas
  • History and Social Studies > Place > Asia
  • History and Social Studies > U.S. > Postwar United States (1945 to early 1970s)
  • Critical analysis
  • Developing a hypothesis
  • Discussion
  • Essay writing
  • Evaluating arguments
  • Historical analysis
  • Making inferences and drawing conclusions
  • Map Skills
  • Oral presentation skills
  • Representing ideas and information orally, graphically and in writing
  • Role-playing/Performance
  • Textual analysis
  • Using primary sources
  • Visual analysis
  • Vocabulary
  • Writing skills
  • John Moser, Ashland University (Ashland, OH)
  • Lori Hahn, West Branch High School (Morrisdale, PA)


Activity Worksheets