Parliament raised taxes on the colonies after the French and Indian War because the British government was in debt.
During the French and Indian War, British prime minister William Pitt allowed the British military to spend as much money as they wanted in order to defeat the French in North America. This ultimately lead to significant debt for the British govenrment.
The British government turned to the colonists to pay off this debt, as they felt it was only fair that the colonists pay for the protection the British military provided the colonists against the French. However, the colonists did not respond well to these taxes because they had no representation in Parliament. This is why the colonists cried "no taxation without representation" in protest of the British government. This would become one of the main reasons for the colonists declaring independence from the British empire.
The incident that started the Sepoy Rebellion was related to a rumor about the the Army using animal fat (especially that of bigs) to grease the inside of bullet cartridges.
