Born in rural Connecticut, Allen had a frontier upbringing but also received an education that included some philosophical teachings. In the late 1760s he became interested in the New Hampshire Grants, buying land there and becoming embroiled in the legal disputes surrounding the territory. Legal setbacks led to the formation of the Green Mountain Boys, whom Allen led in a campaign of intimidation and property destruction to drive New York settlers from the Grants. When the American Revolutionary War broke out, Allen and the Boys seized the initiative and captured Fort Ticonderoga in May 1775. In September 1775 Allen led a failed attempt on Montreal that resulted in his capture by British authorities. First imprisoned aboard Royal Navy ships, he was paroled in New York City, and finally released in a prisoner exchange in 1778.