The first true test of the Cold War erupted in 1950, and for six months combat raged up and down the Korean peninsula before settling into years of trench warfare.
Aug. 15, 1945
An agreement following the end of World War II divides Korea - formerly annexed by Axis power Japan - into U.S. and Soviet occupation zones along the 38th Parallel. The split keeps the country's original capital city, Seoul, in the south.
May 10, 1948
In the Republic of Korea (ROK), the U.S-backed, 70-year-old Korean expatriate Syngman Rhee is elected chairman of the Korean Assembly, and later becomes president. The Communist Party in the north, led by 33-year-old Kim Il Sung, forms the People's Republic of North Korea (DPRK) - backed by China and the Soviet Union.
U.S. Secretary of State Dean Acheson says that America's western defense perimeter cuts through the Sea of Japan and includes the Philippines and former WWII foe Japan, but stops short of including South Korea. Historians believe this gave North Korea a green light to invade the South and create a unified communist state.
June 25, 1950
After a year of military provocations by both sides along the 38th Parallel, North Korea sends an invasion force into South Korea. Northern forces overwhelm the ill-equipped defenders and capture Seoul in three days. The United Nations condemns the attack and creates a "police" force to help defend South Korea.
July 5, 1950
The first U.S. Marines - leading the U.N. force - join battle shortly after landing on the Korean Peninsula. U.S. troops suffer heavy casualties and the four American divisions are driven back into a perimeter around the southern port city of Pusan.
Sept. 15, 1950
U.S. Gen. Douglas MacArthur - commander of the U.N. forces - makes a bold military move and lands an amphibious invasion force of 80,000 Marines at the port of Inchon near Seoul. The tactical move cuts off North Korean troops, while U.N. forces break out of the Pusan perimeter.
Sept. 26, 1950
Seoul is taken by U.N. forces after two weeks of house-to-house fighting. MacArthur orders troops to continue chasing the retreating North Korean army across the 38th Parallel.
Oct. 19, 1950
U.N. forces capture the North Korean capital of Pyongyang, which sits 90 miles northwest of the 38th Parallel.
Oct. 25, 1950
MacArthur continues to sweep confidently onward, his U.N. forces pushing North Korean troops up to the Yalu River - the water border with China. Some U.N. forces actually reach the river, where they are attacked by small groups of Chinese communist soldiers.
Nov. 25, 1950
China, issuing warnings against the U.N. that it should cease aggressions against North Korea, sets a trap to crush MacArthur's army. Chinese forces, numbering 130,000 to 300,000, invade North Korea and push U.N. troops southward in a disorganized, hasty retreat.
Nov. 7-Dec. 9, 1950
With their backs to the Sea of Japan and fighting in a brutally cold winter, U.S. Marines encircled at the Chosin Reservoir retreat to the ports Hungnam and Wonsan, where some 20,000 troops and refugees are evacuated. Known as the battle of "Frozen Chosin," the Chinese route 15,000 U.N. troops, causing 12,000 casualties; of those, 3,000 are killed.
Nov. 30, 1950
U.S. President Harry S. Truman threatens to use the atomic bomb against the communist Chinese forces. By April 5 of the next year, the U.S. Joint Chiefs of Staff ordered atomic retaliation against Soviet and Chinese bases if more communist troops entered the war.
Jan. 4, 1951
As U.N. troops continue to retreat back across the 38th Parallel, the North Korean army recaptures Seoul. The Chinese-North Korean army is stopped by U.N. troops 30 miles south of Seoul and begin a counteroffensive by the end of January.
March 18, 1951
The South Korean capital of Seoul changes hands for the last time as U.N. troops recapture the battered city. MacArthur's army advances slightly north of the 38th Parallel.
April 11, 1951
Because of their disagreement in how to militarily handle the Korean War, President Truman recalls MacArthur as commander of the U.N. forces, and U.S. Gen. Matthew Ridgeway is given command.
July 10, 1951
Truce talks begin at Kaesong near the 38th Parallel. The talks, led by U.S. Vice Admiral C. Turner Joy for the U.N. side and Lt. Gen. Nam Il of North Korea, drag on with no real agreements on an armistice and exchange of prisoners. The truce site is moved to the village of Panmunjom.
The war along the 38th Parallel becomes a stalemate reminiscent of trench warfare fought in World War I. The pattern of bloody fighting with no real capturing of territory continues for the next two years as peace talks repeatedly fail.
Oct. 8, 1952
Talks at Panmunjom deadlock and are recessed. U.S. planes bomb the North Korean capital Pyongyang for two straight months. Talks are resumed the following March.
July 27, 1953
The U.N., North Korea and China sign an armistice agreement, continuing the division of Korea. South Korea refuses to sign. The agreement calls for a 2.5-mile-wide buffer zone across the middle of the Korean Peninsula that closely follows the 38th Parallel.