The Vermont War was an armed conflict between the Vermont Republic and the United States of New England on one side, and the Republic of New York and volunteers from New Jersey and several Iroquois tribes on the other. The war broke out in November 1789 when New York ordered troops into the Vermont (which was under dispute between New York and the New England state of New Hampshire), which ultimately lead to the participation of New England. The Vermont War was the first conflict fought within the former United States of America, which dissolved only a year prior.
The war was fought primarily within the Vermont Republic, but also extended as far west as the Hudson River (which Vermont claimed as the border). The Vermont War was also noted as a turning point in New York's relationship with the Iroquois tribes within the state. Mohawk Chief Joseph Louis Cook (who served as a colonel under George Washington) would lead the attack of mostly Iroquois men against Vermont troops at the Battle of the Hudson in 1790.
The war officially ended in August 1791 with the signing of the Treaty of Providence, in which Vermont's independence was recognized by New York. New York also agreed to relinquish its claims to the disputed territories west of the Great Lakes, provided that New England (particularly Massachusetts) relinquish all land claims west of Lake Champlain and east of the Great Lakes.
After the conflict, the Vermont Republic ultimately became a state of New England. Shortly after that, New York and New Jersey united into the Union of New Netherland. The war left both New England and New Netherland into having bitter relations throughout the majority of the 19th century. Several years after the conclusion of the Vermont War, the Northwest War would take place between New England and Virginia.