The British parliament put new taxes on American colonists after 1763 due to the amount of debt the British developed during the French and Indian War. During the French and Indian War, the British and American colonists fought together to defeat the French. However, the British military spent way more money than they anticipated.
Since the British parliament felt that they spent this money to protect the American colonists, they should be responsible for helping to pay for this war. This was just the beginning of a series of taxes that would lead to the American Revolution.