Pennsylvania ( (listen) PEN-səl-VAY-nee-ə; Pennsylvania German: Pennsilfaani), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, and Appalachian regions of the United States. It borders Delaware to the southeast, Maryland to the south, West Virginia to the southwest, Ohio to the west, Lake Erie and the Canadian province of Ontario to the northwest, New York to the north, and the Delaware River and New Jersey to the east. Pennsylvania is the fifth-most populous state in the nation with over 13 million residents as of 2020. It is the 33rd-largest state by area and ranks ninth among all states in population density. Nearly half the population (6.09 million) is concentrated in the southeastern Delaware Valley metropolitan area, centered around Philadelphia, the state's largest and nation's sixth most populous city; another one-third of the state's residents live in Greater Pittsburgh (2.37 million) in the southwest. Pennsylvania's three largest cities are Philadelphia (1.6 million), Pittsburgh (302,971), and Allentown (125,845). Other major cities include Erie, Reading, Bethlehem, and Scranton. The state capital is Harrisburg. Pennsylvania's geography is highly diverse: the Appalachian Mountains run through its center, while the Allegheny and Pocono Mountains span much of the northeast; close to 60% of the state is forested. While it has only 140 miles (225 km) of waterfront along Lake Erie and the Delaware River, Pennsylvania has more navigable rivers than any other state, including the Delaware, Ohio, and Pine Creek. Pennsylvania was one of the thirteen British colonies that would eventually form the United States. The state was founded in 1681 through royal land grant to William Penn, son of the state's namesake; the southeast portion was once part of the colony of New Sweden. Established as a haven for religious and political tolerance, the Province of Pennsylvania was noteworthy for its relatively peaceful relations with native tribes, innovative government system, and religious pluralism. Philadelphia hosted the first and second Constitutional Convention that ultimately supported, inspired, and led the American Revolution and an ultimately successful quest for American independence. Pennsylvania's governing framework inspired both the Declaration of Independence, which historian Joseph Ellis has described as "the most potent and consequential words in American history", and the U.S. Constitution. Both documents were drafted and ultimately ratified in Independence Hall in Philadelphia, on July 4, 1776 and June 21, 1778, respectively. Pennsylvania became the second state (after Delaware, which had previously been a part of Pennsylvania as the three lower counties) to ratify the Constitution on December 12, 1787.During the American Civil War, Pennsylvania's 360,000 Union Army volunteers proved influential in strengthening the Union, successfully guarding the national capital of Washington, D.C. following the fall of Fort Sumter, and later leading daring raids against Confederate Army strongholds in the Deep South. The bloodiest battle of the Civil War with over 50,000 casualties, and one of the Union Army's most important victories, was fought on Pennsylvania soil at Gettysburg over three days in July 1863. Lincoln's 272 word address dedicating Gettysburg National Cemetery on November 19, 1863 remains one of the best known speeches in American historyIn the late 19th and 20th centuries, Pittsburgh-based U.S. Steel, Bethlehem-based Bethlehem Steel, and other Pennsylvania companies inspired the Industrial Revolution and contributed to the development of much of the nation's early infrastructure, including key bridges, skyscrapers, and warships, tanks, and other military hardware that proved vital to U.S.-led victories in World War I, World War II, and the Cold War. Since Pennsylvania's 1787 founding, a sizable number of influential Pennsylvanians have contributed significantly in nearly all fields, including the military, politics, business, science and innovation, thought leadership, music, art, professional and Olympic sports, and other fields.