On this day, December 16, 1773, one of the most iconic events in American history took place, with a group of colonists taking direct action against the British government by boarding their ships and destroying all of the tea on board by dumping it into Boston Harbor. The colonists were angered when Boston officials refused to return three shiploads of taxed tea to Britain.

From Wikipedia:

The Tea Party was the culmination of a resistance movement throughout British America against the Tea Act, which had been passed by the British Parliament in 1773. Colonists objected to the Tea Act for a variety of reasons, especially because they believed that it violated their right to be taxed only by their own elected representatives.

While The Tea Party had managed to prevent the unloading of taxed tea in three other colonies, in Boston, Royal Governor Thomas Hutchinson refused to allow the tea to be returned to Britain. As a result, what has become known as "The Boston Tea Party" became one of the key events in American history, that eventually lead to the American Revolution.

For more information, please refer to the above referenced Wikipedia article.