Why did Great Britain raise taxes on American colonists?

To help pay the expenses of the French and Indian War ~ apex

King George III borrowed money from other countries to pay for the Seven Years' War (also known as the French and Indian War in North America) and had to pay them back.

In order to cover some of the £60m (and still rising) spent on the Seven Years' War -- which the British said had been fought partly to protect the colonists -- Prime Minister George Grenville asked Parliament to tax the colonists.

At the time, taxation was in excess of a tenth of British national income against a few per cent in the colonies, and politicians in London hoped to spread the burden. It was old-fashioned British penny-pinching rather than a monstrous plot to subvert colonial self-government, but that wasn't how American opponents saw it.