The Korean War

Contextual Background

By: Brad St. Croix

Brad St. Croix

Historical Contributor

Brad St. Croix is a freelance historian and researcher. He earned his PhD in history from the University of Ottawa. His dissertation examined the legacy of the Battle of Hong Kong in Canada. He has also written numerous articles for the Juno Beach Centre and the Canadian Military History Journal. He has worked on public history projects with several organizations including the RCAF Foundation, the Royal Canadian Regiment Museum, the Canadian War Museum, and Project 44. He runs the OTD Military History social media accounts and YouTube channel.

Sign reading, “”Warning, 38th degree North Latitude 100 yards North””. 1951. Image courtesy of the United Nations Photo.


On June 25, 1950, the military of the Democratic People’s Republic of Korea (North Korea) crossed the 38th parallel and invaded the Republic of Korea (South Korea). The same day, the United Nations condemned the attack and passed UN Security Council Resolution 82, calling for the cessation of hostilities and the withdrawal of North Korean forces.

How did a small-scale civil war become an international confrontation that saw Canadian troops fight for the first time in East Asia since the Battle of Hong Kong in 1941? To begin to answer this question, we must understand the situation in Korea and the world geopolitical situation more broadly in the 1940s leading into 1950.


A system of control over a former enemy’s colony with the proposed goal of future independence and self-governance for the colony’s peoples.

Korea, a once unified nation that had been occupied by the Japanese since 1910, became a subject of importance at the Yalta Conference in February 1945, where Allied leaders met to determine how the world would be organized following an anticipated Allied victory to end the Second World War. The Soviet Union shared a border with Korea and sought to control the peninsula in the absence of Japanese power. After intense debate, Joseph Stalin agreed to enter the Soviet Union into war with Japan (the other Allied powers had all been at war with Japan since late 1941) and to support a trusteeship system in Korea following the war, the latter an idea introduced by American President Franklin Roosevelt. The United States and the Soviet Union would each hold a trusteeship of one half of Korea after the Japanese were defeated.

As the Second World War neared its conclusion, Soviet forces reached northern Korea (having previously invaded Japanese-occupied Manchuria), while American troops arrived in the south to secure the surrender of Japanese troops there. The Americans and Soviets divided the Korean peninsula along the 38th parallel; the north would be under Soviet control and the south under American. The aim of the division was to eventually reunite the country under one government after a free and open election. This was not to be.

Franklin D. Roosevelt, Churchill, and Stalin at the Livadia Palace in Yalta, February 9, 1945. Image courtesy of the American National Archives Catalog.

Broader International Relations

Rhee’s dictatorial control over South Korea ended in 1960 due to the April Revolution, when student-led demonstrations over election fraud called for Rhee’s resignation. A high number of demonstrators were killed trying to suppress the protests. The National Assembly unanimously voted to remove Rhee, who resigned on April 27 1960, and went into exile in Hawaii.

Following Rhee’s resignation South Korea’s government was marked instability with military coups, assassinations, and further repressive governments. By the late 1980s, reforms began to take place leading to the first civilian president, Kim Young-Sam, in over thirty years.

Following a rapid deterioration of Soviet–American relations after the Second World War ended, neither side was willing to allow any situation in Korea that might strengthen its adversary. There were attempts to reach an agreement to unite the peninsula, but a year and a half of negotiations failed to produce agreement on a representative group of Koreans to form a provisional government. As a result, both countries began to set up governments friendly to themselves in their areas of control.

Portrait photo of Dr. Syngman Rhee, c. 1939. Photo credit: Harris & Ewing. Image courtesy of the Library of Congress.

Yielding to American pressure, the UN supervised and certified the partial elections that took place in the south alone in May 1948, resulting in the formation of South Korea in August 1948. The Soviet Union sponsored the creation of North Korea in September 1948. Both governments claimed sovereignty over all of Korea.

In the south, President Syngman Rhee installed a repressive, dictatorial, and anti-Communist regime, while wartime guerrilla leader Kim Il Sung imposed the Stalinist model on the north. Stalinism was defined by centralized control of the economy, state terror, authoritarianism, and a cult of personality around the leader. This system still dominates North Korea today. With official governments in place in both new nations, American and Soviet troops began withdrawing their troops by the end of 1948.

After the North Korean Crossing of the 38th Parallel

There has been much debate about who among the communist leaders (Joseph Stalin, Mao Zedong, and Kim Il Sung) came up with the idea to invade South Korea. Ultimately, however, the responsibility for the invasion lies with Kim Il Sung. Throughout 1949, he consistently asked Stalin for support in an invasion of South Korea. At an April 1950 meeting, Kim gained Stalin’s support if Mao Zedong approved. Shortly thereafter in May, Kim met with Mao in China and also received the Communist Chinese leader’s support for the invasion.[i] On June 25, 1950, North Korea invaded South Korea, launching coordinated attacks at various points along the 38th parallel.

Kim Il-Sung speaks at a rally for the local elections in North Korea held on November 3, 1946.

Following the North Korean invasion, the UN took actions to support South Korea. A core goal of the UN was to provide a forum in which nations could work together to avoid war; this would be the first true test of this purpose. On the same day as the North Korean invasion, UN Security Council Resolution 82 passed. It called for an “immediate cessation of hostilities” and “upon the authorities in North Korea to withdraw forthwith their armed forces to the 38th parallel.”[ii] North Korean leaders ignored the resolution.

Two days after the invasion, on June 27, the UN Security Council passed Resolution 83, which declared that North Korean actions constituted “a breach of peace” and recommended that UN members provide assistance to South Korea to repel the North Korean attack and restore peace on the Korean Peninsula.[iii] Resolution 83 passed the UN Security Council vote seven to one. The Republic of China (based in Taiwan), Cuba, Ecuador, France, Norway, the United Kingdom, and the United States all voted in favour of the resolution. Egypt, India, and the Soviet Union abstained from the vote. Only Yugoslavia voted no.[iv]

It should be noted that the measures to defend South Korea were able to pass the UN Security Council because of the Soviet boycott. As a permanent member of the Security Council, the Soviets had the power to unilaterally veto any resolution. However, six months before the vote, the Soviet Union had left the Security Council to protest the UN’s refusal to seat the People’s Republic of China on the Security Council as a permanent member instead of the Republic of China, the US-backed regime based in Taiwan. The Soviets believed that because the Communists (led by Mao Zedong) had defeated the Nationalists in the Chinese Civil War, they should hold the seat and not the Republic of China. The Soviets could not exercise their veto power without ending the boycott. Official UN support for South Korea could not have happened without the Soviet boycott.

American Influence and Response

Portrait photo of Harry S. Truman. Image courtesy of the American National Archives Catalog.

The UN response to the North Korean invasion of the south was driven by American policy and doctrine. Cold War assumptions governed the immediate reaction of US leaders, who believed that Stalin had ordered the invasion to spread communism. The initial American response was not to commit ground troops. President Harry S. Truman hoped that the South Korean military would defend itself with primarily indirect American assistance. As the North Korean advance continued, American involvement was increased. On June 30, 1950, Truman reluctantly sent American ground troops to Korea after General Douglas MacArthur, the American occupation commander in Japan, advised that failure to do so meant certain destruction of South Korea.

American actions surrounding the invasion of South Korea were guided by the Truman Doctrine. Essentially, this was a policy focused on the containment of communism. Before the United States Congress in 1947, Truman pledged American “support for democracies against authoritarian threats.”[v] The doctrine originated with the primary goal of containing Soviet geopolitical expansion during the early Cold War and also expanded to other communist powers that included North Korea.

On July 7, 1950, the UN Security Council created the United Nations Command (UNC). This command structure would lead UN forces in Korea. The Security Council called on Truman to appoint a UNC commander. The president immediately named General MacArthur, who was required to submit periodic reports to the UN on war developments. Despite the force coming under the UN banner, MacArthur answered directly to Truman and the American military leadership. The UNC still exists today and remains under command of the US military.

General view of the Security Council during the meeting of June 27, 1950, on which the Revised Draft Resolution -concerning the complaint of aggression upon the Republic of Korea- was submitted to the Council by the American Government, and adopted by a vote of seven against two, and two abstentions. Image courtesy of the United Nations Photo.

UN Military Response

The UN response was a coming together of many international nations. Sixteen UN members provided combat troops. They are listed in order of their deployment in Korea: United States, United Kingdom, Australia, Netherlands, Canada, France, New Zealand, Philippines, Turkey, Thailand, South Africa, Greece, Belgium, Luxembourg, Ethiopia, and Colombia. Collective security influenced these nations to send combat troops to the Korean peninsula. Sweden, India, Denmark, Norway, and Italy provided medical support and humanitarian aid. The UNC was the world’s first attempt at collective security under the UN system.

U.S. Marines engaged in street fighting during the liberation of Seoul, c. late September 1950. Image courtesy of U.S. Naval History and Heritage Command.

A Brief Overview of the Korean War

The initial North Korean advance into South Korea was very successful. Seoul, South Korea’s capital, was captured on June 28, 1950, by North Korean forces. The North Korean forces, who were armed with Soviet weapons and vehicles, easily pushed back the lightly armed South Koreans. Soon after, American and South Korean forces were pushed into the Pusan (now Busan) Perimeter. On September 15, 1950, US forces landed at Inchon, behind the North Korean lines. This surprise landing allowed the UN forces at Pusan to break out and force the North Koreans to retreat behind the 38th parallel.

UN forces moved into North Korea, and by November 1950 they had reached the Chinese border at the Yalu River. In response, the Chinese People’s Volunteer Army attacked UN forces and pushed them south of Seoul in early 1951. A UN counteroffensive in spring 1951 pushed Chinese and North Korean forces out of Seoul, and the fighting stabilized around the 38th parallel. It was during this offensive that Canadian soldiers of the 2nd Battalion, Princess Patricia’s Canadian Light Infantry regiment fought in the hills above the Kapyong Valley. The 2nd Battalion, the Royal 22nd Regiment, the famed Van Doos, fought at Hill 355 in November 1951, as did the 1st Battalion, The Royal Canadian Regiment in October 1952. These battles are discussed at length in the “Canadians in Combat” article.

The overall fighting in Korea remained static near the 38th parallel until an armistice was signed on July 27, 1953. This agreement brought most of the fighting to an end. There have been minor border skirmishes since the armistice was signed, but no large-scale fighting has taken place. An uneasy peace still exists on the Korean peninsula.

United Nations flag flying over post near the Imjin River, Korea, February 1952. Image courtesy of Library & Archives Canada.

[i] “The Korean War 101: Causes, Course, and Conclusion of the Conflict,” in Association for Asian Studies,

[ii] “Resolution 82 (1950) / [adopted by the Security Council at its 473rd meeting], of 25 June 1950,” in United Nations Digital Library,

[iii] “Resolution 82 (1950) / [adopted by the Security Council at its 473rd meeting], of 25 June 1950.”

[iv] “Security Council resolution 83 (1950) [on assistance to the Republic of Korea],” in United Nations Digital Library,

[v] “The Truman Doctrine, 1947,” in US State Department, Office of the Historian,