The Quakers (also called Friends) were immigrants who came to the colonies in the 1600s to escape persecution in England for their religious beliefs. In 1700s, at the time of the American Revolution, only two colonies tolerated Quakers - Rhode Island and Pennsylvania. Other colonies did not welcome Quakers. They found their ways too strange and too passive for the times.
The Quakers were opposed to violence in any form. But their passive resistance in the American Revolution was most helpful in swaying the opinions of non-Quaker people, even some who normally would have mocked and laughed at their quiet ways. Some colonists believed that if the gentle Quakers were against taxation without representation, perhaps this British policy needed another look.
The Stamp Act moved the Quakers to the forefront of resistance. They actively boycotted British goods.
The Friends (Quakers) encouraged their members to stand fast for liberty and to resist in peaceful ways every attempt to deprive any colonist of liberty.
But this did not mean the Quakers encouraged or condoned violence.
Quoted from: The Religious Affiliation of War General Nathanael Greene: From: Matthew Baltz, "Nathanael Greene and the American Revolution" on official website of Harwich Public Schools, Cape Cod, Massachusetts
His heritage stems from Quaker immigrants five generations prior, who left Salisbury, England in 1635 to escape persecution for their religious beliefs. His father, also named Nathanael, was a respected minister among the Society of Friends, as well as the owner of a series of forge, grist and saw mills... Greene showed an unusual interest in the military for a Quaker. On September 30, 1773, Greene was cast out of a meeting with the Society of Friends for attending a 'place of Publick Resort,' namely, a military parade.
Later, on July 20, 1774, at the age of 32, Greene married Catherine Littlefield, a young, non-Quaker woman nineteen years of age... The decision to join the militia was not without consequences, for taking up arms was strictly against his pacifistic Quaker heritage...
Greene's story is one that should always be remembered, for without the self-sacrificing service of the 'Fighting Quaker' from Rhode Island, the country may not have finally gained its independence over 200 years ago."