Battles between British troops and colonial militiamen in Lexington and Concord in April 1775 kicked off the armed conflict, and by the following summer, the rebels were conducting a full-scale war for their independence
1 Answer
Literally "initiated", that is, "started off".
It's idiomatic, the metaphor being the "kick-off" of a football ("soccer") match. "Kick off" is when the team who won the toss are first to "kick" (that is, to prod with a boot) the ball into play.