The colonists already were not happy with Great Britain. They had been taxed by Great Britain before and thought it was entirely unfair, as they had nobody in the British Parliament to vouch for them. This is known as "taxation without representation."
When the Quartering Act of 1765 got put onto the colonists, this only made them angrier and resent Great Britain even more. The Quartering Act made it so the colonists would be forced to house British troops. Not only this, but they would have to feed them, give them transportation, wash their clothes, and other things the colonists hated.
If I were a colonist, I would be upset. The Quartering Act was an invasion of privacy and they were being taxed to pay for barracks for the troops.
