Final answer:
Mercy Otis Warren was a Massachusetts-born patriot who actively opposed British measures by publishing anti-British works and eventually a three-volume history of the American Revolution.
Step-by-step explanation:
Mercy Otis Warren became a patriot because she actively opposed British reform measures before the outbreak of fighting in 1775 by publishing anti-British works. Born in Massachusetts, Mercy Otis Warren was a prominent writer and intellectual who used her talents to support the American Revolution. In 1812, she took a further step by publishing a three-volume history of the American Revolution, which she began in the late 1770s, boldly entering into the public sphere that was at the time dominated by men.