The Sons of Liberty were a grassroots group of instigators and provocateurs in colonial America who used an extreme form of civil disobedience—threats, and in some cases actual violence—to intimidate loyalists and outrage the British government. The goal of the radicals was to push moderate colonial leaders into a confrontation with the British Crown.

The Sons marked one of their early victories in December 1765. The Stamp Act—the first tax imposed directly on American colonists by the British government—had only been in effect for a month, when a group of Boston merchants and craftsmen sent a letter to Andrew Oliver, the newly-appointed official collector of stamps. The group informed Oliver that he was to show up the next day at noon at the Liberty Tree in the city’s South End to publicly resign.

“Provided that you comply with the above, you shall be treated with the greatest Politeness and Humanity,” the letter explained. The message left to Oliver’s imagination what terrible fate might befall him if he didn’t comply.

Oliver didn’t need much persuading. He appeared as demanded, walking through the streets of Boston in a driving rainstorm and quit his job, to the cheers of a crowd of 2,000 people.

It was an exhibition of the fearsome clout of the Sons of Liberty. The Sons likely formed from a secretive group of nine Boston-based patriots who called themselves the Loyal Nine. The first Sons chapters sprung up in Boston and New York City, but other cells soon appeared in other colonies as well.

The group may have taken its name from a speech given in Parliament by Isaac Barre, an Irish member sympathetic to the colonists, who warned that the British government’s behavior “has caused the blood of these sons of liberty to recoil within them.”

Their most famous act of disobedience was destroying 92,000 pounds of British tea in Boston Harbor in December 1773. The Boston Tea Party, as the act would become known, was one of the key events that pushed the colonies and the British government toward war.

The Sons’ most prominent leader was Samuel Adams, the son of a wealthy brewer who was more interested in radical rabble-rousing than commerce. Adams wrote his masters thesis at Harvard on the lawfulness of resisting British rule. While George Washington eventually led the war effort against the British, “the truth is that there might not have been a fight to begin with had it not been for the work of Sam Adams,” writes historian Les Standiford.

Another key member was John Hancock, who later was immortalized by his flamboyant signature on the Declaration of Independence. James Otis, Paul Revere, Benedict Arnold, and Dr. Benjamin Rush, among others, were also involved in the group.

Adams and Hancock in particular were so loathed and feared by the British that when General Thomas Gage offered amnesty to Bostonians who stopped their resistance in 1775, he made a point of excluding the two men, “whose offences are of too flagitious a nature” not to be punished severely.

It’s not hard to understand why Gage took a hard line against them. After forming in the summer of 1765, the Boston Sons chapter marched through the streets and burned stamp officer Oliver’s effigy, and then broke into and looted his house. When Massachusetts Lt. Gov. and Chief Justice Thomas Hutchinson, a loyalist, declined to renounce the Stamp Act, they similarly looted and destroyed his house as well.

The Sons didn’t stop there. After Parliament passed the Townshend Acts in 1767, which imposed import duties on goods such as china and glass, Adams organized a boycott to keep British goods out of Massachusetts altogether. According to Adams biographer Dennis Fradin, the Sons enforced the boycott by sending boys to smash the windows and smear excrement on the walls of local shops that didn’t comply. If that didn’t work, the proprietor faced the risk of being kidnapped and tarred and feathered, a painful, humiliating torture that could leave lasting scars.

“Violence was not necessarily accepted as a regular feature of politics, but there was an understanding that it might be part of politics as a last resort,” explains Benjamin L. Carp a historian at Brooklyn College and author of the 2010 book Defiance of the Patriots: The Boston Tea Party and the Making of America.

During this time, the Sons’ core views evolved, Carp says. They rejected the British notion that they had fought the French and Indian War on behalf of the colonists, and that as a result, the Americans were obligated to pay for continued upkeep of British soldiers in North America. But beyond that, they also rejected the authority of the British Parliament to make laws for Americans. Most of all, they argued the British government could not compel Americans to pay taxes.

Their overarching goals similarly shifted over time. “At the outset, most Sons of Liberty only wanted something limited—for Parliament to repeal the Stamp Act,” Carp explains. “But over time, more and more Sons of Liberty became convinced that independence was the answer.”

Parliament’s passage in December 1773 of the Tea Act, which propped up the financially struggling British East India Company by giving it a virtual monopoly on selling tea to the colonies, pushed the Sons to become even more brazen. The law threatened the livelihood of the American merchants who had been importing tea from Dutch traders. The Sons couldn’t let that stand.

“I don’t think the Bostonians set out to destroy property. I think they felt it was a last resort,” Carp says. “Their first preference would have been to send the tea back. But when the merchants (consignees) were unwilling, the ship captains were unwilling—it would have ruined them—and the governor was unwilling to bend the rules for them, they felt they had no choice.”

“If they’d allowed the tea to land, they knew that customers wouldn’t be able to resist it—so they would have paid the tax on it AND let a monopoly company, the East India Company, muscle into the local market,” Carp says.

The Bostonians also knew that if they let the tea be unloaded, they’d lose standing in the eyes of other Sons of Liberty groups in New York, Philadelphia and other places, he notes.

The Sons’ defiance of the British not only helped spur the Revolutionary War, it also fostered an American tradition of grassroots activism that various activist groups have applied over the centuries to push for change.