On the night of March 5, 1770, British soldiers fired their muskets into a violent crowd in Boston. Five towns-people died, and the Sons of Liberty, opposing the growth of royal authority, proclaimed the event a "massacre." Condemned in the American press, the Boston Massacre became a major colonial grievance against the London government.

The gunshots in Boston followed seventeen months of friction between locals and British troops deployed to protect royal customs officials. In "A Journal of These Times," a series of one-sided reports sent to other colonies' newspapers in 1768–1769, Bostonians complained about British "redcoats" starting fights, insulting women, and encouraging slaves to revolt. To Whiggish colonists, such episodes reinforced their conviction that "standing armies"—troops maintained by kings in peacetime—were potential oppressors. These disputes coincided with Boston merchants' efforts to enforce a boycott on imports from Britain and thus...