Spotswood worked to make peace with his Iroquois neighbours, winning a concession from them in 1718, of all the land they had conquered as far as the Blue Ridge Mountains and south of the Potomac. This was confirmed at Albany in 1721. This clause was to be a bone of contention decades later, as it seemed to make the Blue Ridge the new demarcation between the Virginia Colony and Iroquois land. But the treaty technically stated that this mountain range was the border between the Iroquois and the Virginia Colony's "Tributary Indians." White colonists considered this license to cross the mountains with impunity, which the Iroquois resisted. This dispute, which first flared in 1736 as Europeans began to settle the Shenandoah Valley, came to a head in 1743. It was resolved the next year by the Treaty of Lancaster, settled in Pennsylvania.