Because King George and the British Empire was in something of a financial crisis. The war had drained them of funds and they found it to be in their best interest to tax the former British citizens. Of course, they didn't really pay much and a lot was overlooked.
There were debts that needed to be paid back from the French and Indian war
King George III taxed the American colonists to raise funds for the British debt incurred during the French and Indian War and to pay for the maintenance of British troops in America. The imposition of several tax acts without colonial representation sparked significant resistance among colonists. This opposition eventually contributed to the American Revolution.
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