By july of 1950 north korean forces had pushed south korean forces as far south as

By July of 1950, North Korean forces had pushed South Korean forces as far south as Pusan.

Explanation:

The Korean War began when North Korea invaded South Korea. The United Nations, with the United States as its main force, came to the aid of the South Koreans. China, in turn, intervened in favor of the north, with the Soviet Union providing them with logistical and political support.

Korea was ruled by Japan from 1910 until the end of World War II. In August 1945, the Soviets declared war on the Japanese as a result of an agreement with the United States and liberated the north of Parallel 38. US troops soon moved to occupy the southern part of the peninsula. In 1948, as a result of the outbreak of the Cold War between the United States and the Soviet Union, Korea was divided into two regions, with separate governments. Representatives of the southern (capitalist, American-influenced) and northern (communist, Soviet-influenced) states each claimed to be the legitimate government of Korea, and neither side accepted the borders of the time as permanent. The conflict escalated into a total open war when the North Koreans, bellied by the Soviets and the Chinese, invaded the south on June 25, 1950. At that time, the United Nations Security Council recognized this as an illegal invasion and demanded a ceasefire. On June 27, the UN Council adopted Resolution 83, condemning the invasion and dispatching a troop under the United Nations flag to restore peace in the Korean peninsula. About twenty-one countries committed military forces to the UN mission, with 88 percent of those soldiers actually being Americans.  

After two months of war, it seemed that South Korea would be overwhelmed by the North Koreans. However, UN forces, mainly made up of US troops, detained the communists on the Pusan perimeter. In September 1950, the Allies launched a counteroffensive on Incheon and imposed a major setback on the North Korean army. Utilizing its military superiority and resources, the United States and its allies continued to force the North Koreans to retreat beyond their own borders, prompting China to take action by sending its armies across the Yalu River, officially entering in the war in favor of the north. This forced UN forces to back down.