After hostilities began in 1861, the Union Armies found limited success in the theaters in the War. Fighting at this stage was largely confined to the area of Northern Virginia between the capitals of Richmond and Washington in the East, and along the broader Mississippi and Ohio River Valleys in the Western theater. The only place with significant Union victories was along the Mississippi and Ohio River Valleys.

In 1867, the Russian Empire was convinced that it would lose its possessions in America due to problems stemming from the Crimean War. Anxious to recoup some value, the Russian Czar negotiated a treaty with US Secretary of State William Seward. The United States, in what critics called Seward's Folly, bought what would become the state of Alaska for $7.2 million.

The Indian Removal Act of 1830 was a large part of Andrew Jackson's efforts to clear out more land in the South for white settlers who were increasingly moving into lands claimed by Native Americans. While Jackson claimed he could take the land as the executive, the Supreme Court overruled him. Nonetheless, Jackson still moved the Cherokee and Creek Tribes to Oklahoma Territory in what is known as the Trail of Tears.

The War of 1812 was seen as a source of national pride for the young American nation--and a sideline to the serious business of the Napoleonic Wars by the British. Most of the initial causes of the war for the Americans directly related to British conduct during the Napoleonic Wars, including detaining sailors heading to French ports, seizing goods from American ships, and violating American territorial claims in Canada.

The Gadsden Purchase acquired nearly 30,000 square miles of the southern portion of the present day states of New Mexico and Arizona, settling territorial disputes stemming from the Treaty of Guadalupe Hidalgo in 1846. The largest backers of the Gadsden Purchase were Southern political leaders, who saw the land as an opportunity to build a transcontinental railroad from the Southern states to California. While the purchase was successful, the railroad never got built across the land.

During 1876, the U.S. pursued a policy of forcing Native American tribes on the Great Plains onto reservations, which was widely opposed by many groups. The Army sent a large Cavalry force, led by General George Armstrong Custer and accompanied by scouts from the Crow tribe, to seek out a combined force of Arapaho, Northern Cheyenne, and Lakota Sioux in Wyoming and Montana. On June 25, 1876, the two armies met at the Little Bighorn River in southern Montana, where an overwhelming force led by the Sioux chief Sitting Bull destroyed Custer's troops, killing the General and much of his staff.

The above quote was spoken by President John Adams. During his Presidential administration many people were clamoring for war with France—the XYZ Affair had offended American national sensibilities, and many politicians in particular felt that warfare was necessary to restore national honor. Adams resisted this feeling though, steadfastly refusing to sacrifice American boys for an unnecessary war.

President James Monroe elucidated what became known as the Monroe Doctrine in 1823 during his seventh State of the Union Address. Worried about European colonial powers desiring to either retake their newly independent former possessions in Latin America or to promote their own interests, Monroe vowed that the United States would intervene on behalf of the newly independent states. The actual Monroe Doctrine was largely authored by John Quincy Adams, Monroe's Secretary of State and successor as President in 1825.

The Monroe Doctrine was first stated by President James Monroe in his seventh State of the Union address to Congress in 1823. Written by Secretary of State John Quincy Adams, the Monroe Doctrine was crafted in response to Latin American revolutionary movements against European colonial powers. The Monroe Doctrine forcefully argued that it was in America's best interests to assist Latin American nations whose sovereignty was threatened by European nations.

In the early Republic, leaders like Tecumseh and Osceola fought state and territorial militias, siding with the British in the War of 1812. After the Civil War, conflicts against Indians increased in the Western territories of the United States. Sitting Bull and Crazy Horse defeated General Custer at Little Bighorn, but surrendered to US forces in the late 1870s. Geronimo and the Apaches continued fighting the US Cavalry in the Southwest until ultimately surrendering in 1886.