On April 19, 1775, the royal military governor sent a detachment of troops to seize gunpowder and arrest local leaders in Concord. At Lexington, Massachusetts, shots broke out with the Lexington militia, leaving eight colonists dead. The British failed to find their targets in Concord, and as they retreated back to Boston, the British came under continuous assault by upwards of 3,800 militia who had prepared an ambush. The Battle of Lexington and Concord ignited the American Revolutionary War. As news spread, local shadow governments (called "committees of correspondence") in each of the 13 colonies drove out royal officials and sent militiamen to Boston to besiege the British there.