Why did colonists dump tea into Boston Harbor?

Colonists dumped tea into Boston Harbor on the night of December 16, 1773 to protest the Tea Act of May 1773 and reject the principle that Parliament could tax them without their consent. The Tea Act gave the East India Company a near monopoly on tea sales in North America by allowing it to ship directly through hand-picked consignees, including relatives of Governor Thomas Hutchinson in Boston. Although the Act actually lowered the retail price of legal tea below smuggled Dutch tea, it preserved the three pence per pound Townshend duty payable in colonial ports.

To Boston's revolutionary leaders, that retained duty was the entire point. If colonists drank the cheap legal tea, they would in practice acknowledge that Parliament had authority to tax them, and Lord North's ministry could later raise duties on any commodity it chose. The argument was constitutional rather than commercial. Colonists also worried that the monopoly precedent would let Britain destroy independent merchants and smugglers and ultimately reorganize colonial commerce around favored cronies.

After the three tea ships arrived in Boston Harbor in late November and early December 1773, Sons of Liberty leaders Samuel Adams, John Hancock, Paul Revere, and others held mass meetings at the Old South Meeting House drawing perhaps 5,000 people, more than a third of Boston's population. They demanded that the ships return to England with their cargo, but Massachusetts customs law required the tea to be unloaded and duty paid within 20 days of arrival, after which the cargo would be seized and sold. Governor Hutchinson refused to grant the clearance papers needed to return the ships to England.

With the deadline at hand, the meeting dispersed and roughly 60 disguised men boarded the ships at Griffin's Wharf and destroyed 342 chests of tea worth about £9,659. Boycotts and tea destruction also took place in Charleston, New York, Philadelphia, and Annapolis between 1773 and 1774, but Boston's event drew the heaviest British retaliation because Massachusetts had been the leader of resistance for years. The destruction was a deliberate political act meant to make impossible the quiet absorption of a parliamentary tax through low prices, and it succeeded.

Britain treated the event as criminal vandalism rather than political protest, and Parliament's response in the Coercive Acts of 1774 confirmed for many colonists that conciliation with London was no longer possible.