They were mad because King George III didn't give them a choice on taxes, and back in England he didn't give them any voice. It's called 'taxation without representation' and it's not fair. So the colonies complained, including one act called the Boston Tea Party, which was where colonists dressed as Native Americans dumped 342 chests (90,000 pounds) of tea into Boston harbor, to show anger. There were many other things that lead to the Revolutionary War. Hope I helped! :D