During the American Revolution the battles fought on Pennsylvania's frontier were more complicated and savage than those waged along the eastern seaboard.

Map of Pennsylvania's disputed borders

Support of the struggle for independence came slowly to the Scots-Irish and German settlers who lived on the Pennsylvania frontiers. Until 1774, they tended to be more concerned with the immediate problems of boundary disputes and frontier defense, problems that they blamed on the provincial government in Philadelphia, which paid only reluctant attention to these issues. After Parliament's passage of the Intolerable Acts, however, settlers in the Pennsylvania backcountry quickly formed radical committees of correspondence and committed fully to the Revolutionary cause.

Pennsylvania's frontiers were ripe for conflict. The original Royal charters of Connecticut, Virginia, and Pennsylvania all had vague and overlapping boundaries that led to disputes over millions of acres.

“The Allies–Par Nobile Fratrium," 1780.

When the American Revolution broke out, these long-standing boundary disputes and decades of simmering hostilities between frontier settlers and Native Americans burst into brutal and bloody warfare. This warfare also undermined the Pennsylvania backcountry's local biases by uniting the Scots-Irish and German settlers who fought a three-pronged war - against the British, Indians, and immigrants from Virginia and Connecticut - and by tying them more closely to the state government in Philadelphia that before the war had been so distant and unresponsive to their concerns.

The conflicts with Native Americans and Pennsylvania's neighboring colonies caused by vaguely defined boundaries had begun in the late 1600s. Connecticut had claimed the northern half of Pennsylvania under its "sea-to-sea" charter of 1662. In the early 1760s, land-hungry Connecticut settlers led by Colonel John Franklin had begun flowing into the Wyoming Valley. The Penn family protested and in 1763 British authorities required Connecticut to prevent any further settlement of its residents in the disputed territory.

At the same time the Penns made land grants to Pennsylvania settlers on the condition that they defend the territory against Connecticut claimants. This triggered a series of "Yankee-Pennamite Wars" that began when Connecticut Yankees mobilized their forces at Fort Durkee in 1769, and then escalated after the Pennamites constructed and manned Fort Wyoming in 1771. The Yankee-Penamite Wars lasted throughout the Revolutionary period, ending in 1784. During the American Revolution, many Iroquois, hoping to secure their own control of the area, joined forces with British Rangers and laid waste to white settlements in the Wyoming Valley.

"Massacre at Wyoming," by Alonzo Chappel, 1858.

Southwestern Pennsylvania was also contested territory on the eve of Independence. Virginia had long claimed access to the headwaters of the Ohio River under its own 1609 "sea-to-sea" charter. In 1774, Virginia's governor, Lord Dunmore, exploited Indian conflicts in the area to solidify that claim. At Augusta Town, in present-day Washington County, settlers claimed land under Virginia's jurisdiction that they made a district in Virginia's Augusta County. There, too, they organized the first county court west of the Monongahela River.

Of all Pennsylvania's boundary disputes, however, those with the Indians were most prolonged and severe. Originally, the Algonquian tribes who inhabited Pennsylvania enjoyed friendly relations with the early European settlers, especially William Penn, whose proprietorship of the colony marked the beginnings of a unique friendship based on mutual trust and respect. But after his death in 1718, Penn's sons, anxious to enhance their personal wealth and power, cheated the Indians out of their lands through notorious acts like the Walking Purchase of 1737. Five years later, the Penns allied with Iroquois to drive the Delaware out of their lands in the Susquehanna valley.

A View of Fort Robertdeau, in Sinking-Spring Valley, State of Pennsylvania,"...

During the next fifteen years, the Penn family's alliance with the Iroquois resulted in significant land acquisitions. Settlers moved into Schuylkill, Carbon, Dauphin, Northumberland, Columbia, and Luzerne Counties, pushed west to the Allegheny Mountains, and from Centre County south to the colony's boundary with Maryland. During the French and Indian War, the Delaware and Shawnee, still bitter over the Walking Purchase, attacked frontier settlements to avenge their losses. This undeclared conflict worsened after the end of the war when the Proclamation Line of 1763 prohibited white settlement west of the Appalachian Mountains. In the Susquehanna Valley, Scots-Irish settlers registered their disapproval of Indian neighbors by slaughtering neutral Conestoga Indians near Lancaster in 1764.

Brant Thayendanegea, by Charles Willson Peale, 1797.

After the Revolutionary War broke out, the simmering hostility towards the Indians became white hot because of the divided allegiances of various tribes. To create a second military front against the rebelling colonies, in May 1776 the British held a conference at Fort Niagara, where they succeeded in gaining the support of many tribes, including many Iroquois and Delaware. To counteract the alliance, the Pennsylvania legislature and the Continental Congress called an Indian conference at Easton in January, 1777. Although Iroquois gave assurances of their intentions to remain neutral, they conducted sporadic raids across the northern tier of Pennsylvania and in nearly every western county during the next few years.

Pennsylvania's northeastern frontier, still divided over the Yankee-Pennamite land conflict, also became a hotly contested battleground between whites and Indians. Savage hit-and-run attacks by joint British and Iroquois forces culminated in a massacre of Pennsylvania militiamen and civilians at the Battle of Wyoming in July 1778.

Title page and engraving, Affecting History of the Dreadful Distresses of Frederic...

Known as the "surpassing horror of the American Revolution," this devastating patriot defeat left the northern frontier open to depredations, and forced Continental authorities to assemble an army large enough to break the power of pro-British Indians.

In June of 1779, Gen. John Sullivan assembled 2,500 Continental forces at Easton, and then marched them to Fort Wyoming on the Susquehanna River. After another month of mobilization and preparation, the army marched up the East Branch of the Susquehanna through Tioga, and into New York. On August 29th, Sullivan's forces defeated Col. John Butler's Rangers and 1,500 Indians under Joseph Brandt at Newtown. From there, Sullivan marched north, destroying Iroquois towns and all the orchards, fields and crops that surrounded them. Sullivan's Campaign weakened the eastern tribes so severely that they never seriously threatened Pennsylvania's frontier again.

Between 1780 and the end of the war in 1783, Pennsylvania's frontier settlers continued to suffer sporadic raids by Indians, especially in the western counties. The torture and death of Colonel William Crawford by the Sandusky Indians in 1782 fueled Pennsylvanians' desire to rid the state of its last native inhabitants. The last threat of Indian resistance would end in 1795, when Gen. Anthony Wayne's victory at the Battle of Fallen Timbers, in present-day Ohio, secured control of Pennsylvania's northwestern territories.

By the end of the war, Pennsylvania had won control of the disputed areas in the northeast, and received title to most of the disputed lands in western Pennsylvania, except for what is now the "panhandle" of West Virginia. The bloody and vicious guerilla warfare that erupted on Pennsylvania's frontiers during the War for American Independence reinforced white racist attitudes towards Native Americans, and emboldened Pennsylvanians to press their land claims on the frontier against Native Americans and neighboring states.

After the war was over, the state also used lands recently held by Indians to pay veterans for their service in the Continental Army. It also sold tens of thousands of acres to enterprising land speculators, who hoped to increase their personal wealth by reselling those lands at a hefty profit. By the 1790s the Commonwealth had also extinguished all Indian claims to their lands within the state.