The area that is now eastern Pennsylvania was originally claimed by the Swedish and Dutch. In 1664, however, James, Duke of York, commanded British forces to remove the Dutch from the Hudson and Delaware Valleys.

After securing control of much of the present-day Mid-Atlantic, King Charles II of England issued one of the largest land grants in recorded history to William Penn in 1682. The land-grant was issued in part to pay off a debt owed to Penn's father. Penn named the area "Pennsylvania, " meaning "Penn's Woods" as a colony of religious tolerance for Quakers. The atmosphere of tolerance quickly attracted Scottish, Irish, and German immigrants, who helped to make Philadelphia the largest city in the all the colonies and the legislative center of Pennsylvania.

As Pennsylvania's burgeoning population began moving west in the 1700's, along with northbound travelers from Virginia, conflict ensued between the colonists and the French. Both parties had claimed the same land in the Ohio Valley (present-day Pittsburgh and points south and west). Military conflict ensued when George Washington and a small detachment attacked a French garrison at the Battle of Jumonville Glen in 1754. Washington, anticipating a French counterattack, quickly ordered the construction of Fort Necessity near present-day Farmington. On a rainy July 3, 1754, French forces of 600 soldiers and 100 Indians attacked, occupied, and burned Fort Necessity to the ground. Washington and his soldiers. however, were allowed to peacefully withdraw from the fort. This marked the first military conflict of the French and Indian War.

In the 1760's and 1770's, Philadelphia became a center of the Patriot cause before and during the American Revolution. Following the issuance of the Intolerable Acts, the First Continental Congress met in Philadelphia's Carpenter's Hall in 1774. A year later, the Second Continental Congress met. On July 4, 1776, Thomas Jefferson's Declaration of Independence wasadopted by members of the Second Continental Congress. This landmark document, written in Philadelphia's Independence Hall, (then called the Pennsylvania State House) officially proclaimed America's intention to become a free and independent nation from Great Britain. Although Great Britain captured Philadelphia in 1777, and forced Congress to relocate to York, Pennsylvania, it was reclaimed by Patriot forces in 1778. Several major battles of the war occurred in or around Philadelphia such as The Battle of Trenton, The Battle of Princeton, and the Battle of Brandywine Creek.

In 1787, delegates from all of the colonies met in Philadelphia to revise the new nation's crumbling government under the Articles of Confederation. On September 17, 1787, in what came to be known as the Constitutional Convention, a brand new Constitution was adopted. On December 12, 1787, Pennsylvania became the second state to ratify it.

In the early 1800's, cities in central and western Pennsylvania began to develop. By 1845, the manufacturing center of Pittsburgh, located on the confluence of the Monongahela, Allegheny, and Ohio Rivers, was one of the largest cities west of the Appalachian Mountains. It would eventually become the nation's largest steel producing center.

After the secession of eleven southern states precipitated the American Civil War in 1861, thousands of Pennsylvanians joined the Union Army. On July 1, 1863, the largest battle ever waged in North America began at a small town known as Gettysburg. It was the only major battle of the Civil War to be fought north of the Mason-Dixon Line. Gettysburg is generally thought of as the turning point of the Civil War, or, the point from which the Union began their offensive. In November of 1863, president Abraham Lincoln dedicated a national cemetery at Gettysburg during his famous Gettysburg Address.

For much of the late 1800's and 1900's, Pennsylvania became one of the nation's industrial centers. Many of the state's larger cities became steel-producing or coal-mining centers, crucial to America's success in World War II. In 1889, the Johnstown Flood resulted in the deaths of over 2,200 people. It was one of the initial disasters overseen by the American Red Cross. In 1894, Milton Hershey founded the Hershey Corporation, which would become one of the world's major chocolate producers. In 1907, the world famous Hershey Park was built.

Today, Pennsylvania is the nation's sixth most populous state. It remains an important industrial center, however, with the decline of the steel industry in America, Pennsylvania has been forced to turn to other industries. Some cities, such as Pittsburgh, have been successful in transforming their economy from industrial to technological and biomedical, while others have crumbled.