Final answer:
The Korean War started with the North Korean invasion of South Korea on June 25, 1950. This led to U.S. involvement under the domino theory and a United Nations-backed military response. The portrayal of the war in international textbooks remains a subject of contention, notably regarding how some Japanese texts describe historical events.
Step-by-step explanation:
The start of the Korean War is generally attributed to the invasion of South Korea by North Korean forces on June 25, 1950. As depicted in various textbooks, after World War II, Korea was divided into a Northern communist government established by the Soviets with Kim Il-sung at the helm, and a Southern authoritarian nationalist regime supported by the United States with Syngman Rhee as leader. Despite South Korea not being considered crucial to U.S. security, President Truman, subscribing to the domino theory, believed in supporting South Korea to prevent the spread of communism and protect Japan.
Significant controversies surround the portrayal of the Korean War in international textbooks. For instance, South Korean protests against Japanese middle school textbooks allege that these texts gloss over negative events like the forced sexual slavery of Korean women during World War II. The textbooks' descriptions tend to downplay Japanese colonial brutalities and other important incidents in Korean history.
The Korean War had a profound impact on U.S. foreign policy, establishing precedents such as military engagement without direct Congressional approval and a commitment to prevent the spread of communism through force. The conflict ended with the division of Korea remaining intact though at high human costs, with an estimated 2 to 3 million Korean fatalities and 35,000 U.S. soldier deaths.