During the American colonial era, the colonies of New York and Connecticut often disputed the precise location of their shared border, leading to a border dispute that eventually gave the colonies their modern shapes. Though the dispute was officially resolved in 1731, effects of the boundary conflict persisted until well after both colonies gained statehood as part of the United States following the American Revolution.
Background
The dispute originated largely as an extension of a wider ongoing conflict between the colonial ambitions of benefactors of the Dutch Republic and the Kingdom of England. Much of the Dutch jurisprudence was based on the writings of the legal scholar Hugo Grotius, who emphasized claiming the land and interaction with the natives. The English did not generally accept Grotius' theories, in particular his Mare Liberum. When Henry Hudson had first explored the area in 1609, he was employed by the Dutch, so the Netherlands could base its claim on both first discovery and status as financial backer. In addition, the Dutch felt “that territorial possession depended on recognition of the rights of indigenous people in regard to their territory as well as on a Dutch military presence to defend the claim from European incursion.” While the majority of the Dutch population of New Netherland clustered around the Hudson River and western Long Island, the Dutch still maintained forts and trading posts along the Connecticut River (e.g., Fort Hoop, in modern-day Hartford) and went on frequent expeditions to exploit the natural resources of the area (e.g., beaver hunting).
By contrast, the exploding population of the neighboring New England Colonies placed ever more farms and settlements across Connecticut and Long Island Sound. Connecticut Colony also based its claims on conquest. Following the end of the Pequot War in 1638, Connecticut had signed a treaty with the Massachusetts Bay Colony and the Mohegan and Narragansett tribes ceding all of the Pequot lands to Connecticut. The English also rejected the claim that Hudson's discovery secured the area for the Dutch: Hudson was an Englishman and had not been hired to explore the area, but had rather discovered it by accident.
Another English objection to Dutch control was based in dealings with the natives. The English believed the Dutch had endangered the "adjoining Countries most wickedly, feloniously, and traitorously, contrary to the Marine and Admirall Laws of all Christians, [by selling] wholesale guns, powder, shot and ammunition to the Indians, instructing them in the use of our fights and arms." The Dutch claim to the land was further weakened when Peter Stuyvesant justified trading guns by citing pressure from the natives.
Treaty of 1650 between New Netherlands and Connecticut
In 1650, the Treaty of Hartford sought to set the border between New Netherlands and the colonies of Connecticut. The main land was split by a line 50 miles from the Connecticut River and Long Island was divided into an East (Connecticut) and West (New Netherland) at Oyster Bay. However, the treaty was never ratified back in England, which left the border unresolved when the Province of New York was created by a sea-to-sea grant in 1664, just two years after Connecticut had been issued a sea-to-sea charter in 1662.
The colonies of New York and Connecticut
Governor Nicolls and the 1664 agreement
The settlers from Connecticut and New York jostled over their respective claims. Long Islanders who had arrived from New England were very resistant to becoming New Yorkers. Local government under the Duke's charter gave no guarantee of assembly or “other privileges to which [New Englanders] had become accustomed.”
In 1664, Charles II of England sent royal commissioners, led by Gov. Nicolls, in part to “end unneighbourly and unbrotherly contentions” about the borders. The commissioners met with John Winthrop and Connecticut commissioners in November 1664.
As part of the agreement, announced in December 1664, the main land was divided “by the consent” of the commissioners with a north-northwest line at the mouth of the Mamaroneck River. Long Island, which was explicitly mentioned only in the grant to the Duke of York, was entirely given to New York. Though nominally an agreement, the “language of the agreement, however, gave it the character of a declaration or order to which Connecticut submitted as a subordinate.”
