Why were colonist upset about paying taxes?

Because themselves with little interference. But in the 1760's, Britain began to tighten their control over the colonies.

After the french and Indian war, Britain lost lots of money, so Britain thought the colonists should pay their share. They were mad not only it was a lot of money to pay, they were taxed on things they really needed and enjoyed, like tea, sugar, and legal documents. They also made them house and feed the British soldiers (red-coats) and they closed the Boston harbor controlling trade. The colonists were furious. They said, "no taxation without representation!" In April 1775, war broke out between the colonists and Britain. The American revolution had begun.

hope i helped :)