This Day in History — American History

On June 25, 1929, President Herbert Hoover authorized the construction of Boulder Dam, later renamed Hoover Dam. The massive project helped control the Colorado River, generate hydroelectric power, and supply water to the growing American Southwest, becoming one of the greatest engineering achievements in United States history.

On June 24, 1853, President Franklin Pierce approved the Gadsden Purchase, acquiring nearly 30,000 square miles from Mexico for $10 million. The agreement established the modern U.S. border in the Southwest, supported plans for a southern transcontinental railroad, and marked the final major territorial expansion of the contiguous United States.

On June 19, 1865, Union troops arrived in Galveston, Texas, and announced the freedom of enslaved African Americans more than two years after the Emancipation Proclamation. Known as Juneteenth, the day symbolizes emancipation, resilience, and the long journey toward equality, later becoming a federal holiday in 2021.

On June 17, 1915, former President William Howard Taft helped establish the League to Enforce Peace at Philadelphia’s Independence Hall. Advocating collective security and international cooperation, the organization proposed peaceful dispute resolution among nations and helped lay the intellectual foundation for the League of Nations and later the United Nations.

On June 15, 1775, the Continental Congress appointed George Washington commander-in-chief of the newly formed Continental Army. Chosen for his military experience and ability to unite the colonies, Washington's leadership proved crucial during the American Revolution and helped guide the colonies toward eventual independence from Great Britain.