The Green Mountain Boys were a group of pseudo-guerrilla paramilitary fighters in Vermont. The group was founded in Bennington in 1770 to protect the land claims of settlers from New Hampshire.
Before the revolution, Vermont did not exist as a separate entity. Instead, it was claimed by both New Hampshire and New York, who were bitterly trying to outdo each other to administrate the land. Governor Wentworth of New Hampshire sent settlers out into Vermont, and gave them charters for their settlements that he technically wasn't allowed to give. In response, the government of New York sent troops to these towns, and told the settlers that they had to pay New York for the land New Hampshire had given them.
Several New Hampshire settlers gathered at Fay's Tavern in Bennington in 1770, and formed the Green Mountain Boys. They were led by Ethan Allen, a land speculator from Connecticut and a fierce supporter of the New Hampshire land claims. New York immediately issued a warrant for Allen's arrest, but New York was unable to enforce the warrant. The Green Mountain Boys soon found themselves the de facto government and army in the area. Officials and settlers from New York were harassed, beaten, and driven out of the area.
When the American Revolution began in 1775, Ethan Allen led the Green Mountain Boys on a surprise attack of British-held Fort Ticonderoga, on the New York side of Lake Champlain. They were able to capture the fort without firing a shot, as the British garrison was unaware that the war had even begun. The boys then gave the cannons at the fort to George Washington to help in the assault on Boston.
Ethan Allen was so emboldened by his success at Fort Ticonderoga, he accepted a proposal from General Schuyler and General Montgomery to invade Canada. However the Green Mountain Boys elected Seth Warner as their leader, and decided to stay put. Those who chose to march to Montreal with Allen were captured and imprisoned with him when the plan of attack failed miserably.
When Vermont declared its independence, the Vermont Army was modeled after the Green Mountain Boys. The Boys continued to fight on the American side of the Revolution, participating in the Battles of Hubbardton and Bennington. As Vermont began to slide towards a more neutral stance, more and more of the Green Mountain Boys decided to join the Continental Army instead. By the time Vermont was admitted as a state in 1791, the Green Mountain Boys were all but dissolved.