Pennsylvania, officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Maryland to its south, West Virginia to its southwest, Ohio and the Ohio River to its west, Lake Erie and New York to its north, the Delaware River and New Jersey to its east, and the Canadian province of Ontario to its northwest via Lake Erie. Pennsylvania’s most populous city is Philadelphia.

Pennsylvania was founded in 1681 through a royal land grant to William Penn, the son of the state’s namesake. Before that, between 1638 and 1655, a southeast portion of the state was part of New Sweden, a Swedish colony. Established as a haven for religious and political tolerance, the colonial-era Province of Pennsylvania was known for its relatively peaceful relations with native tribes, innovative government system, and religious pluralism.

Pennsylvania later played a vital and historic role in the American Revolution and the ultimately successful quest for independence from the British Empire, hosting the First and Second Continental Congress in Philadelphia, which formed the Continental Army and elected George Washington as its commander in 1775 during the American Revolutionary War, and unanimously adopted the Declaration of Independence the following year. In 1787, following the establishment of the nation’s independence, the Constitution of the United States, now the world’s oldest and longest-standing written and codified national constitution, was written at the Constitutional Convention in Philadelphia, and was ratified in Philadelphia the following year. On December 12, 1787, Pennsylvania was the second state to ratify the U.S. Constitution.

In July 1863, during the American Civil War, the Battle of Gettysburg, fought over three days in and around Gettysburg, was the bloodiest battle of both the Civil War and of any battle in American military history, with over 50,000 Union and Confederate casualties. But the success of the Union army at Gettysburg in repelling Confederate general Robert E. Lee’s attempt to invade the North also proved the Civil War’s turning point, leading to the Union’s preservation.