Abraham Lincoln ( LINK-n; February 12, 1809 April 15, 1865) was an American lawyer and statesman who served as the 16th president of the United States from 1861 until his assassination in 1865. Lincoln led the nation through the American Civil War and succeeded in preserving the Union, abolishing slavery, bolstering the federal government, and modernizing the U.S. economy.

Lincoln was born into poverty in a log cabin in Kentucky and was raised on the frontier, primarily in Indiana. He was self-educated and became a lawyer, Whig Party leader, Illinois state legislator, and U.S. Congressman from Illinois. In 1849, he returned to his law practice but became vexed by the opening of additional lands to slavery as a result of the KansasNebraska Act of 1854. He reentered politics in 1854, becoming a leader in the new Republican Party, and he reached a national audience in the 1858 Senate campaign debates against Stephen Douglas. Lincoln ran for President in 1860, sweeping the North to gain victory. Pro-slavery elements in the South viewed his election as a threat to slavery, and Southern states began seceding from the Union. During this time the newly formed Confederate States of America began seizing federal military bases in the south. Just over one month after Lincoln assumed the presidency, the Confederate States attacked Fort Sumter, a U.S. fort in South Carolina. Following the bombardment, Lincoln mobilized forces to suppress the rebellion and restore the Union.

Lincoln, a moderate Republican, had to navigate a contentious array of factions with friends and opponents from both the Democratic and Republican parties. His allies, the War Democrats and the Radical Republicans, demanded harsh treatment of the Southern Confederates. Anti-war Democrats (called "Copperheads") despised Lincoln, and irreconcilable pro-Confederate elements plotted his assassination. He managed the factions by exploiting their mutual enmity, carefully distributing political patronage, and by appealing to the American people. His Gettysburg Address appealed to nationalistic, republican, egalitarian, libertarian, and democratic sentiments. Lincoln closely supervised the strategy and tactics in the war effort, including the selection of generals, and implemented a naval blockade of the South's trade. He suspended habeas corpus in Maryland, and he averted British intervention by defusing the Trent Affair. In 1863 he issued the Emancipation Proclamation, which declared the slaves in the states "in rebellion" to be free. It also directed the Army and Navy to "recognize and maintain the freedom of such persons" and to receive them "into the armed service of the United States." Lincoln also pressured border states to outlaw slavery, and he promoted the Thirteenth Amendment to the United States Constitution, which upon its ratification abolished slavery.

Lincoln managed his own successful re-election campaign. He sought to heal the war-torn nation through reconciliation. On April 14, 1865, just days after the war's end at Appomattox, he was attending a play at Ford's Theatre in Washington, D.C., with his wife Mary when he was fatally shot by Confederate sympathizer John Wilkes Booth. Abraham Lincoln is remembered as a martyr and a national hero for his wartime leadership and for his efforts to preserve the Union and abolish slavery. Lincoln is often ranked in both popular and scholarly polls as the greatest president in American history.

The president of the United States (POTUS) is the head of state and head of government of the United States of America. The president directs the executive branch of the federal government and is the commander-in-chief of the United States Armed Forces.

The power of the presidency has grown substantially since the office's establishment in 1789. While presidential power has ebbed and flowed over time, the presidency has played an increasingly strong role in American political life since the beginning of the 20th century, with a notable expansion during the presidency of Franklin D. Roosevelt. In contemporary times, the president is also looked upon as one of the world's most powerful political figures as the leader of the only remaining global superpower. As the leader of the nation with the largest economy by nominal GDP, the president possesses significant domestic and international hard and soft power.

Article II of the Constitution establishes the executive branch of the federal government and vests the executive power in the president. The power includes the execution and enforcement of federal law and the responsibility to appoint federal executive, diplomatic, regulatory, and judicial officers. Based on constitutional provisions empowering the president to appoint and receive ambassadors and conclude treaties with foreign powers, and on subsequent laws enacted by Congress, the modern presidency has primary responsibility for conducting U.S. foreign policy. The role includes responsibility for directing the world's most expensive military, which has the second largest nuclear arsenal.

The president also plays a leading role in federal legislation and domestic policymaking. As part of the system of checks and balances, Article I, Section 7 of the Constitution gives the president the power to sign or veto federal legislation. Since modern presidents are also typically viewed as the leaders of their political parties, major policymaking is significantly shaped by the outcome of presidential elections, with presidents taking an active role in promoting their policy priorities to members of Congress who are often electorally dependent on the president. In recent decades, presidents have also made increasing use of executive orders, agency regulations, and judicial appointments to shape domestic policy.

The president is elected indirectly through the Electoral College to a four-year term, along with the vice president. Under the Twenty-second Amendment, ratified in 1951, no person who has been elected to two presidential terms may be elected to a third. In addition, nine vice presidents have become president by virtue of a president's intra-term death or resignation. In all, 45 individuals have served 46 presidencies spanning 58 full four-year terms.Joe Biden is the 46th and current president of the United States, having assumed office on January 20, 2021.