The primary trigger for the American Revolutionary War was the imposition of taxes by the British Parliament on the American colonies without their consent, leading to the rallying cry of "no taxation without representation." Events like the Stamp Act of 1765 and the Townshend Acts created significant unrest and resentment among colonists, as they felt their rights were being violated. The situation escalated with incidents such as the Boston Tea Party in 1773, which protested the Tea Act. Ultimately, these grievances culminated in the outbreak of armed conflict in 1775, marking the start of the revolution.