The East India Company was "too big to fail." It had a monopoly on the importation of tea to Britain and thence to her colonies, but the Dutch didn't lay tarriffs or taxes on their tea, and so smuggling Dutch tea, especially in America, was a popular and profitable pastime. Huge surplusses of the stuff began to pile up in British warehouses. What to do - repeal the taxes? Of course not. By virtue of the Tea Act of 1773, the Company would be allowed to ship tea directly to the Americas (cutting out middlemen) and it would be taxed there upon landing. With a brilliant application of crony capitalism, certain favored parties would be granted profitable licenses as tea consignees.
The colonists, especially in that radical hothouse called Boston, had at least two problems with this. First, there was that "taxation without representation" jazz we all read about in fifth grade or so (or should have). More directly, the tax money collected would pay the salaries of royal governors, judges and certain officials (like revenue men) and the local legislatures would lose control of the purse - These men would be unanswerable to the people they governed.
Several ships laden with tons of tea set sail for American ports. Royal governors in New York, Philadelphia and Charleston knew the public sentiment well enough to allow the protesters to force the tea consignees to resign, and to let the ships sail peacefully back to England. Governor Hutchinson of Massachusetts was another matter. He was tired of that loudmouth Sam Adams and that whole bloody lot calling themselves "Sons of Liberty," and it was high time for their comeuppance. Oh, and two of his sons were designated tea consignees - Imagine that... The Dartmouth, the Eleanor and the Beaver were going back emptied of their cargo, and that was that. Turns out the Sons of Liberty agreed, they just differed with the Governor on exactly where the tea was going.
There is a story that Sam Adams triggered the raid on the tea with the codewords "This meeting can do nothing further to save the country!" announced before a large crowd at the Old South Meeting House. Whether this is true or whether he simply lost control of the meeting, dozens of the Sons of Liberty dispersed, and then reassembled; many of them wearing old blankets, soot on their faces and feathers in their hair, in a hillarious attempt to look like Mohawks. Nobody was about to mistake these guys for actual Indians - they looked more like a minstrel show caricature. So what was this all about? Obviously they wanted to make it hard to identify individuals, but there was a message they wanted to send - They were AMERICANS now, not merely colonial Englishmen. The Indian was a symbol peculiar to America, and so was the tool they chose for the task at hand; the tomahawk (though some more civilized types could only manage to grab a simple hatchet).
As a raucous crowd cheered them on, they dumped 342 smashed chests of tea into Boston harbor.
The loss of what today would be millions of dollars worth of tea was not about to go unnoticed at Whitehall, and the patriots knew it, but they had seen no other honorable way out:
Last night 3 Cargoes of Bohea Tea were emptied into the sea. This Morning a Man of War Sails. This is the most magnificient Movement of all. There is a Dignity, a Majesty, a Sublimity, in this last Effort of the Patriots, that I greatly admire... This however is but an Attack upon property. Another similar Exertion of popular Power, may produce the destruction of lives... What Measures will the Ministry take, in Consequence of this? Will they resent it? Will they dare to resent it? Will they punish us? How? By quartering troops upon us? by annulling our Charter?
Diary of John Adams, December 17, 1773.
Well John, the answer is "D. All of the above." Local militias began to squirrel away guns, powder and shot. The countdown to bloodshed among erstwhile bretheren had begun.