Over 200 years ago British soldiers marched from Boston to the towns of Lexington and Concord in order to seize weapons that were stored there by the citizens of Massachusetts. The British commander stationed in Boston feared an armed rebellion and wanted to make sure one could not occur and so he sent his troops to take the supply of weapons from the citizens of Massachusetts.
The citizens of Massachusetts thought the British government did not have a right to tell them what to do. The British government was willing to use a large force of professional soldiers in order to make sure the citizens of Massachusetts did what they were told. The citizens of Massachusetts thought that the only way to prevent their rights from being trampled on by a brutal dictator was to take up arms against this occupational force living amongst them.
So when the British soldiers arrived in Lexington on their way to Concord in order to seize the weapons of the Massachusetts citizenry, they were fired upon by citizens of Massachusetts that were willing to fight for freedom from the British government. The battles at Lexington and Concord are the first of the American Revolution.