Nine years after winning independence from Mexico, the Republic of Texas was formally annexed by the United States, becoming the 28th state. Mexico had never recognized Texan independence and viewed annexation as an act of aggression. The dispute over the Texas-Mexico border soon escalated into the Mexican-American War, which would ultimately reshape the map of North America.

Soldiers of the US 7th Cavalry surrounded a band of Lakota Sioux near Wounded Knee Creek to disarm them. A struggle over a rifle triggered a massacre in which troops with rapid-fire Hotchkiss guns killed between 250 and 300 Lakota, many of them women and children fleeing across the snow. The event marked the last major armed conflict between the US Army and Native Americans.