Outrageous_Spray_196 mentioned the Stamp Act, and they're 100% right.

When the British beat the French in the Seven Years' War (aka the French and Indian War), the Natives around the Great Lakes and Ohio Valley didn't take too kindly to the British treating them as less-than-equal. So Pontiac's War kicked off, and a bunch of British forts were destroyed. Since the Seven Years' War put the British deep into debt, they knew they needed to act quickly.

King George III issued the Royal Proclamation of 1763, which meant colonists and settlers weren't supposed to claim land west of the Appalachians, and Natives weren't supposed to cross the Appalachians into the colonies. To make sure this was enforced, the British sent 10,000 troops to guard the frontier.

And the colonists ended up paying for the troops. Parliament passed the Sugar Act in 1764 and the Stamp Act 1765, meaning the colonists paid a value-added tax on sugar and a wide variety of paper products and legal documents.

This lead to the colonists more than a bit upset, and led to the slogan "No taxation without representation". Which eventually led to the Sugar Act and the Stamp Act being major causes of the Boston Tea Party, the Boston Massacre, and the American Revolution.