The United States House of Representatives, usually referred to as the House, is the lower house of the United States Congress, with the Senate being the upper house. Together they compose the national bicameral legislature of the United States.

The House's composition was established by Article One of the United States Constitution. The House is composed of representatives who, pursuant to the Uniform Congressional District Act, sit in single member congressional districts allocated to each state on a basis of population as measured by the U.S. Census, with each district having one representative, provided that each state is entitled to at least one. Since its inception in 1789, all representatives have been directly elected, although universal suffrage didn't come to effect until after the passage of the 19th Amendment and the Civil Rights Movement. Since 1913, the number of voting representatives has been at 435 pursuant to the Apportionment Act of 1911. The Reapportionment Act of 1929 capped the size of the House at 435. However, the number was temporarily increased to 437 when Hawaii and Alaska were admitted to the Union.If enacted, the DC Admission Act would permanently increase the number of representatives to 436. In addition, there are currently six non-voting members, bringing the total membership of the House of Representatives to 441 or fewer with vacancies. As of the 2010 Census, the largest delegation was California, with 53 representatives. Seven states have only one representative: Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont, and Wyoming.The House is charged with the passage of federal legislation, known as bills; those of which that are also passed by the Senate are sent to the president for consideration. The House also has exclusive powers: it initiates all revenue bills, impeaches federal officers, and elects the president if no candidate receives a majority of votes in the Electoral College.The House meets in the south wing of the United States Capitol. The presiding officer is the Speaker of the House, who is elected by the members thereof. The Speaker and other floor leaders are chosen by the Democratic Caucus or the Republican Conference, depending on whichever party has more voting members.

The American Civil War (April 12, 1861 – May 9, 1865; also known by other names) was a civil war in the United States between the Union (states that remained loyal to the federal union, or "the North") and the Confederacy (states that voted to secede, or "the South"). The central cause of the war was the status of slavery, especially the expansion of slavery into territories acquired as a result of the Louisiana Purchase and the Mexican–American War. On the eve of the Civil War in 1860, four million of the 32 million Americans (~13%) were enslaved black people, almost all in the South.The practice of slavery in the United States was one of the key political issues of the 19th century. Decades of political unrest over slavery led up to the Civil War. Disunion came after Abraham Lincoln won the 1860 United States presidential election on an anti-slavery expansion platform. An initial seven southern slave states declared their secession from the country to form the Confederacy. Confederate forces seized federal forts within territory they claimed. The last-minute Crittenden Compromise tried to avert conflict but failed; both sides prepared for war. Fighting broke out in April 1861 when the Confederate army began the Battle of Fort Sumter in South Carolina, just over a month after the first inauguration of Abraham Lincoln. The Confederacy grew to control at least a majority of territory in eleven states (out of the 34 U.S. states in February 1861), and asserted claims to two more. Both sides raised large volunteer and conscription armies. Four years of intense combat, mostly in the South, ensued.

During 1861–1862 in the war's Western Theater, the Union made significant permanent gains—though in the war's Eastern Theater the conflict was inconclusive. On January 1, 1863, Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal, declaring all persons held as slaves in states in rebellion "forever free." To the west, the Union destroyed the Confederate river navy by the summer of 1862, then much of its western armies, and seized New Orleans. The successful 1863 Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Confederate General Robert E. Lee's incursion north ended at the Battle of Gettysburg. Western successes led to General Ulysses S. Grant's command of all Union armies in 1864. Inflicting an ever-tightening naval blockade of Confederate ports, the Union marshaled resources and manpower to attack the Confederacy from all directions. This led to the fall of Atlanta in 1864 to Union General William Tecumseh Sherman and his march to the sea. The last significant battles raged around the ten-month Siege of Petersburg, gateway to the Confederate capital of Richmond.

The Civil War effectively ended on April 9, 1865, when Confederate General Lee surrendered to Union General Grant at the Battle of Appomattox Court House, after Lee had abandoned Petersburg and Richmond. Confederate generals throughout the Confederate army followed suit. The conclusion of the American Civil War lacks a clean end date: land forces continued surrendering until June 23. By the end of the war, much of the South's infrastructure was destroyed, especially its railroads. The Confederacy collapsed, slavery was abolished, and four million enslaved black people were freed. The war-torn nation then entered the Reconstruction era in a partially successful attempt to rebuild the country and grant civil rights to freed slaves.

The Civil War is one of the most studied and written about episodes in the history of the United States. It remains the subject of cultural and historiographical debate. Of particular interest is the persisting myth of the Lost Cause of the Confederacy. The American Civil War was among the earliest to use industrial warfare. Railroads, the telegraph, steamships, the ironclad warship, and mass-produced weapons saw wide use. In total the war left between 620,000 and 750,000 soldiers dead, along with an undetermined number of civilian casualties. President Lincoln was assassinated just five days after Lee's surrender. The Civil War remains the deadliest military conflict in American history. The technology and brutality of the Civil War foreshadowed the coming World Wars.