## Learning Outcomes

- Understand how **containment** became the central U.S. Cold War strategy after World War II
- Identify the roles of **George F. Kennan**, the **Truman Doctrine**, the **Marshall Plan**, and **NSC-68**
- Explain why the Korean War became the first major military test of containment
- Recall the main turning points of the Korean War, including **Inchon**, **Chinese intervention**, and the **armistice at Panmunjom**
- Distinguish between **containment** and **rollback**
- Analyse why Truman fired **Douglas MacArthur** and why that matters for civilian control of the military
- Assess the Korean War’s significance for presidential power, U.S. defense spending, and Cold War globalism

## AP United States History Syllabus

For the AP United States History, you are expected to understand the development of containment and the Korean War as part of Period 8 foreign policy, with a focus on the following syllabus points:

- Know that **containment** aimed to stop the spread of communism rather than overthrow communist governments already in power
- Identify **George F. Kennan’s Long Telegram (1946)** as a key intellectual basis for early Cold War policy
- Understand the **Truman Doctrine (1947)** as U.S. aid to peoples resisting communist pressure, especially in **Greece and Turkey**
- Explain the **Marshall Plan (1948)** as an economic tool of containment in Western Europe
- Know that **NSC-68 (1950)** called for a major military buildup and a more global, militarized containment strategy
- Recall that Korea was divided near the **38th parallel**, and that **North Korea invaded South Korea on June 25, 1950**
- Understand that the Korean War was fought as a **United Nations police action** without a formal congressional declaration of war
- Explain the significance of **limited war**, **MacArthur’s dismissal**, and the **1953 armistice at Panmunjom**

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What did the United States mean by **containment** in the early Cold War?
2. How did the **Truman Doctrine** and **Marshall Plan** differ as methods of containment?
3. Why did the Korean War begin in **1950**?
4. Why did Truman dismiss **Douglas MacArthur**?
5. What is the difference between an **armistice** and a **peace treaty**?

## Introduction

The Cold War from **1945 to 1980** is one of the most important themes in APUSH Period 8, and the subtopic of containment and the Korean War sits near the center of it. After World War II, the United States abandoned older habits of limited overseas involvement and committed itself to resisting communist expansion across the globe. That shift changed U.S. diplomacy, military spending, alliance-building, and presidential power.

The Korean War matters because it was the first major armed conflict fought under this new Cold War mindset. It showed that containment was not just a theory in diplomatic speeches. It could send American troops into battle, raise the risk of wider war with China and the Soviet Union, and reshape U.S. policy for decades.

> **Key Term: containment**
> The Cold War policy of preventing the spread of communism rather than immediately overthrowing communist regimes already in power.

### From wartime alliance to Cold War strategy

At the end of World War II, the United States and the Soviet Union emerged as the two major superpowers. They had cooperated against Nazi Germany, but that alliance rested on necessity, not trust. Once the war ended, their differences became much clearer. The United States supported capitalist economies, political pluralism, and open international trade. The Soviet Union supported communist rule and sought security through influence over Eastern Europe.

This tension sharpened as the Soviets established control over countries such as **Poland**, **Hungary**, and **Czechoslovakia**. American leaders increasingly feared that communist influence would keep expanding if it went unchallenged. That fear was not just ideological. U.S. leaders also believed stable, noncommunist markets were necessary for American trade and prosperity.

> **Key Term: Cold War**
> The long struggle after World War II between the United States and the Soviet Union, marked by rivalry, arms competition, and proxy wars rather than direct full-scale war between the two superpowers.

The intellectual basis for the U.S. response came largely from **George F. Kennan**. In his **Long Telegram (1946)**, Kennan argued that the Soviet Union was expansionist but also cautious. He believed the United States should respond with firm, patient resistance rather than immediate war.

> **Key Term: Long Telegram**
> George F. Kennan’s 1946 message arguing that the Soviet Union should be met with steady, firm resistance, forming a basis for containment.

Containment is easy to define too simply. Students often think it meant “fight communism everywhere with troops.” Early containment was broader than that. At first, it included political pressure, economic aid, and alliance-building. Military force became more central later, especially after **1950**.

A useful distinction is this:

- **Political-economic containment** tried to make noncommunist states more stable and less likely to fall to revolution
- **Military containment** used troops, bases, alliances, and rearmament to resist communist expansion directly

This distinction matters in essays. It shows change over time: containment began as a broad strategy and became more militarized after Korea.

> **Test Tip:** For APUSH causation questions, do not present containment as one fixed policy from day one. Show development: **Kennan → Truman Doctrine → Marshall Plan → NSC-68 → Korean War**.

### Truman Doctrine, Marshall Plan, and NSC-68

The first major public statement of containment was the **Truman Doctrine** in **1947**. Britain could no longer support anti-communist forces in **Greece and Turkey**, so President **Harry Truman** asked Congress for aid. He declared that the United States should support “free peoples” resisting armed minorities or outside pressure.

> **Key Term: Truman Doctrine**
> The 1947 policy stating that the United States would support peoples resisting communist pressure, first applied to Greece and Turkey.

Why was this important? Because it marked a major break from older patterns in U.S. foreign policy. Instead of stepping back after a European war, the United States now accepted long-term global responsibilities. It also framed local struggles as part of a worldwide contest between freedom and communism.

The **Marshall Plan** followed in **1948**. Secretary of State **George Marshall** proposed massive economic aid to rebuild Western Europe. This was containment through recovery, not combat.

> **Key Term: Marshall Plan**
> A U.S. program of economic aid launched in 1948 to rebuild Western Europe and reduce the appeal of communism.

The logic was practical. Economic collapse creates instability. Instability can strengthen radical movements. If Western Europe recovered, communist parties there would have less appeal. This is a good example of how containment was not initially just military. It aimed to shape conditions in which communism would be less attractive.

Then came a further shift. In **1949**, two events increased U.S. anxiety sharply:

- the Soviet Union successfully tested an atomic bomb
- communist forces won the Chinese Civil War, leading to the “loss of China”

By **1950**, the National Security Council produced **NSC-68**, a report arguing that the Soviet threat was global and that the United States needed a major military buildup.

> **Key Term: NSC-68**
> A 1950 National Security Council report calling for greatly increased defense spending and a more militarized global policy of containment.

NSC-68 is a turning point because it pushed containment toward rearmament. Before Korea, such proposals were expensive and politically harder to sell. After Korea began, they became much easier to justify.

This creates a strong APUSH cause-and-effect chain:

- Soviet expansion in Eastern Europe raised U.S. fears
- Kennan provided the strategic framework
- Truman applied it first through aid and rhetoric
- the Marshall Plan used economic recovery as a Cold War weapon
- the Soviet bomb and communist victory in China increased alarm
- NSC-68 argued for military expansion
- the Korean War made that expansion urgent

### Why Korea became the first major test of containment

Korea had been ruled by Japan before **1945**. After Japan’s defeat in World War II, Korea was temporarily divided near the **38th parallel**:

- the **Soviet Union** occupied the north
- the **United States** occupied the south

That division hardened into two rival states. In the north, **Kim Il-sung** led a communist regime backed by the Soviets. In the south, **Syngman Rhee** led an anti-communist government supported by the United States.

> **Key Term: 38th parallel**
> The line near which Korea was divided after World War II into a Soviet-backed North and a U.S.-backed South.

The immediate trigger came on **June 25, 1950**, when **North Korea invaded South Korea**. But for APUSH you should explain both trigger and context. The invasion mattered because of broader Cold War conditions:

- the U.S. had just seen communist victory in China
- NSC-68 had warned of a global communist threat
- American leaders feared inaction would weaken containment everywhere

The United States intervened under the authority of the **United Nations**, partly because the **Soviet Union was boycotting the Security Council** and could not veto action.

> **Key Term: United Nations police action**
> Military intervention in Korea under UN authority, led mainly by the United States, without a formal U.S. declaration of war.

This matters in two ways. First, it reflected the post-1945 move toward collective security. Second, it raised a constitutional issue: Truman committed U.S. troops without asking Congress for a declaration of war.

Students often miss that Korea was a war and a precedent. Truman called it a police action, but it involved large-scale combat and expanded presidential war powers.

> **Test Tip:** If an SAQ or LEQ asks about change in U.S. foreign policy, Korea is strong evidence that the United States had moved away from pre-World War II reluctance and toward permanent global military commitments.

### Turning points in the Korean War and why they mattered

At first, North Korean forces advanced rapidly. South Korean defenders and U.S. troops were pushed back to the **Pusan Perimeter** in the southeast. This early crisis mattered because it showed that containment could fail quickly if the United States did not respond with force.

Then came one of the war’s biggest turning points: **General Douglas MacArthur’s Inchon landing** in **September 1950**. This amphibious landing cut behind North Korean lines and reversed the war’s momentum.

> **Key Term: Inchon landing**
> MacArthur’s September 1950 amphibious assault that helped drive North Korean forces back after early UN setbacks.

After Inchon, U.S. and UN forces moved north across the 38th parallel. At this point the war’s aims changed. What began as defense of South Korea shifted toward reunifying Korea under anti-communist control. This is where students should distinguish **containment** from **rollback**.

> **Key Term: rollback**
> A strategy aimed at pushing communism back out of areas already under communist control, rather than merely stopping further spread.

Advancing north risked provoking **China**, especially as UN forces approached the **Yalu River**, near the Chinese border. China then intervened in late **1950**, sending large forces into the war and pushing UN troops back south.

This transformed the conflict. The war became a stalemate rather than a march to victory. It also exposed a major strategic divide between Truman and MacArthur.

MacArthur wanted to widen the war, including heavier attacks on China and ideas associated with broader anti-communist victory in Asia. Truman rejected this. He feared direct war with China might bring in the Soviet Union and possibly trigger a much wider, even nuclear, conflict.

> **Key Term: limited war**
> A war fought for restricted objectives, avoiding full escalation into a larger or total war.

Truman’s position showed that U.S. goals in Korea were ultimately limited. The aim was to contain communism, not to conquer China. That is why APUSH teachers stress Korea as an example of limited war.

When MacArthur publicly criticized Truman, the president dismissed him in **April 1951**.

This is significant for more than personality. It demonstrates:

- the difference between **limited war** and **rollback**
- the constitutional principle of **civilian control of the military**
- the danger of expanding a Cold War conflict into a wider war

MacArthur remained popular with many Americans, so Truman paid a political price. But from a constitutional perspective, his action reinforced presidential authority over generals.

The fighting dragged on until an **armistice** was signed at **Panmunjom** on **July 27, 1953**.

> **Key Term: armistice**
> An agreement to stop fighting; unlike a peace treaty, it does not formally end the state of war.

The armistice restored a divided Korea near the prewar boundary and created the **DMZ**, or demilitarized zone. The war did not end in reunification, total victory, or a peace treaty.

> **Key Term: Panmunjom armistice**
> The 1953 agreement that stopped fighting in the Korean War and left Korea divided near the prewar line.

A common error is to say the Korean War “ended” in a peace settlement. It did not. Fighting stopped, but no formal peace treaty followed.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- **Containment** was the Cold War strategy of stopping the spread of communism rather than overthrowing existing communist governments
- **George F. Kennan’s Long Telegram (1946)** supplied the intellectual basis for containment
- The **Truman Doctrine (1947)** first applied containment through aid to **Greece and Turkey**
- The **Marshall Plan (1948)** used economic recovery as a nonmilitary form of containment
- **NSC-68 (1950)** called for major military rearmament and a more global containment strategy
- Korea was divided after World War II near the **38th parallel**
- **North Korea invaded South Korea on June 25, 1950**, beginning the Korean War
- The United States intervened under a **UN police action**, not a formal congressional declaration of war
- Major turning points included the **Pusan Perimeter**, **Inchon landing**, advance toward the **Yalu River**, and **Chinese intervention**
- Truman’s firing of **Douglas MacArthur** showed the importance of **limited war** and civilian control of the military
- The **Panmunjom armistice (1953)** stopped fighting but did not create a peace treaty
- The Korean War helped militarize containment, raise defense spending, and expand presidential war powers

## Key Terms and Concepts

- containment
- Cold War
- Long Telegram
- Truman Doctrine
- Marshall Plan
- NSC-68
- 38th parallel
- United Nations police action
- Inchon landing
- rollback
- limited war
- armistice
- Panmunjom armistice


The Cold War from 1945 to 1980 - Containment and Korean War