I'm assuming you're talking about the American Revolution, but if you are indeed not, please correct me so I can correct my answer.
The British treated the colonists badly by taxing them a lot on goods imported from them. The colonists tried to get them to see reason by making numerous petitions against "taxation without representation," but the British King, George III, did not care and continued to tax them. Not only that, when the king heard of the colonist's protests, he sent guards from Britain to patrol the streets all the time. He also forced the colonists to house these guards in their own homes without asking them first. Finally, when a group of protesters protested in Boston, the guards rallied and shot them all, hence why it was called the "Boston Massacre." The colonists finally got fed up with him and started the American Revolution.
I hope this answer helped you! If you have any further questions or concerns, feel free to ask! :)