Slain miner & one of his fighting comrades (Library of Congress)

On the morning of Apr. 20, 1914, members of the Colorado national guard attacked a tent colony of striking mine workers at Ludlow, Colo. During the course of the day, at least five miners, two women, and eleven children were killed, and the encampment was looted and burned. The miners responded over the next several days by arming themselves, attacking a number of mines, driving off or killing the guards, and setting fire to the buildings. The governor called out additional national guardsmen, and federal troops sent by President Woodrow Wilson arrived on Apr. 30. In the fighting between Apr. 20 and 30, at least fifty people, including those killed during the massacre, lost their lives.

Ruins Ludlow Colony, 1914 (Library of Congress)