Conversation so far:
What wars were the Powhatan involved in?
The Powhatan people were involved in the First Anglo-Powhatan War.
What was the First Anglo-Powhatan War about?
Powhatan ordered something like a siege of Jamestown. This was the Indians' best chance to win the war, but the English survived and, after the arrival of reinforcements, viciously attacked.
Were the Powhatan involved in any other wars besides the First Anglo-Powhatan War?
The Powhatan were involved in the Second Anglo–Powhatan War following the First Anglo-Powhatan War.
Who won the Second Anglo-Powhatan War?
The Treaty of 1646 marked the effective dissolution of the united confederacy, as white colonists were granted an exclusive enclave between the York and Blackwater Rivers.

Question: When did they sign a treaty?
Self-contained rewrite: When did the Powhatan people sign a treaty?