The Sons of Liberty was an organization in the 13 colonies dedicated to fighting the Stamp Act through violence or print.
This organization started in the summer of 1765, when a group of shopkeepers and artisans in Boston prepared themselves for an uprising against the stamp act. The reason for this desperate action was that the people didn't like being taxed by the British government.
As more and more people joined, this group (originally called The Loyal Nine) became known as The Sons of Liberty. One of their first actions was to publish a cartoon showing Andrew Oliver, the person who was to be commissioned as Distributor of Stamps for Massachusetts, hanging from a tree with a demon coming out of a boot.
Fired up by this cartoon, a mob burned the poor man's property and then beheaded and burned his effigy and stoned his house. The Sons of Liberty then looted it and left.
However, most of the organization's actions were not violent, such as publishing newspapers without stamps and roasting the Stamp Act in their contents.