Kansas-Nebraska Act (1854) Law sponsored by Illinois senator Stephen A. Douglas to allow settlers in newly organized territories north of the Missouri border to decide the slavery issue for themselves; fury over the resulting nullification of the Missouri Compromise of 1820 led to violence in Kansas and to the formation of the Republican party.
Kellogg-Briand Pact Representatives of sixty-two nations in 1928 signed the pact (also called the Pact of Paris) to outlaw war.

Kentucky and Virginia Resolutions (1798–99) Passed in response to the Alien and Sedition Acts, the resolutions advanced the state-compact theory that held states could nullify an act of Congress if they deemed it unconstitutional.
King William’s War (War of the League of Augsburg) First (1689–97) of four colonial wars between England and France.

King’s Mountain, Battle of Upcountry South Carolina irregulars defeated British troops under Patrick Ferguson on October 7, 1780, in what proved to be the turning point of the Revolutionary War in the South.

Knights of Labor Founded in 1869, the first national union picked up many members after the disastrous 1877 railroad strike but lasted, under the leadership of Terence V. Powderly, only into the 1890s; supplanted by the American Federation of Labor.

Know-Nothing (American) party Nativist, anti-Catholic third party organized in 1854 in reaction to large-scale German and Irish immigration; the party’s only presidential candidate was Millard Fillmore in 1856.

Korean War Conflict touched off in 1950 when Communist North Korea invaded South Korea, which had been under U.S. control since the end of World War II; fighting largely by U.S. forces continued until 1953.

Ku Klux Klan Organized in Pulaski, Tennessee, in 1866 to terrorize former slaves who voted and held political offices during Reconstruction; a revived organization in the 1910s and 1920s stressed white, Anglo-Saxon, fundamentalist Protestant supremacy; the Klan revived a third time to fight the civil rights movement of the 1950s and 1960s in the South.