The United States and North Korea have announced a nuclear-disarmament-for-aid deal after their first nuclear talks since the death of Kim Jong Il. Here’s a timeline of some key developments of North-South tensions in Korean history:

— Sept. 9, 1948: Kim Il Sung establishes the Democratic People’s Republic of Korea in the northern half of the Korean peninsula.

— June 25, 1950: North Korea invades the South, beginning the Korean War. United States backs South Korea, while China and the Soviet Union provide support to the North.

— July 27, 1953: Korean War ends in armistice, not a peace treaty. Demilitarized Zone established along the border; U.S. military presence in South Korea remains....