This wonderful and typically American appellative refers to a prosperous group of ranchers, landowners and speculators whose intention it was to create the US state of Vermont, arising from territory whose ownership was disputed between New Hampshire and New York.
The Green Mountain Boys with their heavily armed employees defied the authority of the government of New York, during the years of the thirteen UK colonies. The gangs harassed and assaulted the pro-British colonists (of whom there were many more than is popularly supposed) in the state of New York, in one of the many bloody insurrections of early America. The movement was one of the few successes obtained by the independence-seeking colonists, before the American Revolution broke out which led to the Declaration of Independence.
When the Revolution came, which was inevitable, the Green Mountain Boys under their leader Ethan Allen re-directed their energetic attentions and helped the colonists capture the British-held Fort Ticonderoga on the freezing Lake Champlain (north New York State) in 1775, a year before the Signers signed. Cannon taken from the fort proved most useful in the subsequent colonial siege of British-occupied Boston in Massachusetts.