What event did the british start to impose new taxes on the american colonists? why?

The British government was deeply in debt after the Seven Years War (French and Indian War in the colonies). At the same time, they did not want new conflicts to arise in territories taken from the French. The Proclamation of 1763 banned expansion of the colonies beyond the Appalachian Mountains.

As the British people were already burdened by taxes, Parliament decided to levy taxes on the colonies, which were previously not taxed. The colonists were ticked off, as they had no representation in Parliament.