Native American Property Rights and European Contact

Despite the claim to rights based on discovery, British colonists often acquired land by contract. For example, almost all of Massachusetts was acquired by purchase from local tribes. The primary exceptions there, Salem and Boston, were uninhabited areas, having been depopulated earlier by the diseases the colonists unwittingly brought with them. Although the British crown claimed the sole right to negotiate transfer of land rights from the Native Americans, many colonists thought otherwise and regularly made individual arrangements with various tribes to secure land.

This is from Europe Meets America, a heavy post in the Freeman.