The local militia at Concord and Lexington had no national government at the time British troops marched into their towns, so they were all the military force that existed at the time. The American Civil War was different from the American Revolution in that militiamen North and South rarely ever saw action. Also, even though militia commands did carry a substantial part of the load in the Revolution, Congress still set a standard that a militiaman had to prove six months service to qualify for pension support.
To follow your Concord and Lexington militia analogy, when U.S. troops entered New Orleans, the 1st Native Guards battled them from street to street in the city, fighting and dying from one block to the next. If I read your post correctly, that must have actually happened - right?