England heavily taxed its North American colonies because of response to the financial costs for Indian war and French.
The indian and French war was part of a big conflict which was referred to as seven years war.
The war ranged across North America and Europe and this forced England to empty its treasury so as to win.
England decided to make their taxes high on colonist in America which made them to have financial strain.
So this raised a lot of tension between the colonists and England.