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The United States of America takes title to the Louisiana Purchase, which stretches the United States from the Canadian border to the mouth of the Mississippi River.
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Ordered by Thomas Jefferson to map the Northwest United States, Lewis and Clark begin their expedition from St. Louis and Camp Dubois. The journey begins with navigation of the Missouri River.
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U.S. President James Madison asks Congress to declare war on the United Kingdom. Before the vote could be approved, on June 16, British ships raise a blockade against the United States.
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The Missouri Compromise bill, sponsored by Henry Clay, passes in the United States Congress. This legislation allows slavery in the Missouri territory, but not in any other location west of the Mississippi River that was north of 36 degrees 30 minutes latitude, the current southern line of the state of Missouri.
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The United States to annex the Republic of Texas and led to the United States adding the Republic of Texas into the Union as the 28th state.
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The Pony Express begins. Overland mail between Sacramento, California and St. Joseph's, Missouri is carried over the Oregon Trail for eighteen months by this series of riders on horseback, then rendered obsolete when the transcontinental telegraph is completed.
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Fort Sumter in Charleston, South Carolina harbor is bombarded for 34 hours by Confederate forces after the U.S. Army commander failed to evacuate, thus starting the four years of conflict and the U.S. Civil War.
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The Homestead Act is approved, granting family farms of 160 acres (65 hectares) to settlers, many of which were carved from Indian territories.
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The Thirteenth Amendment, abolishing slavery, takes effect.
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The 20th President of the United States, James A. Garfield, is shot by lawyer Charles J. Guiteau in the Baltimore and Potomac Railroad station in Washington, D.C.
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The Statue of Liberty arrives for the first time in New York harbor.
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Women in Colorado are granted the right to vote.