Three sects of Protestant pacifists came together in colonial Pennsylvania to give it a character that continues to color the state today: the Quakers, the Mennonites and the Amish. All three share a common origin because they faced religious persecution by dissenting from religious conformity in the 16th and 17th centuries. However, that aside, the origins of the Mennonites and Amish are quite distinct from that of the Quakers.
The Religious Society of Friends, or Quakers, began as a movement of nonconformists. This was a general movement of Protestants who wanted to break out of the English brand of Puritanism. From their foundation in the 1650s, the Quakers were persecuted in the British Isles and the New England colonies. Then term "Quaker" stems from a patronizing jibe on the part of an English judge that the Friends "tremble at the word of God." The Friends turned it around and started using the term themselves, although their formal name has always remained the same. Quaker core beliefs include "testifying" to four ideals in everyday life: pacifism, simplicity, equality and honesty.
The Mennonites are named for their founder Menno Simons. They evolved from the Anabaptist movement of Holland and Germany during the violent years of the Reformation and Counter-Reformation. Simons was a Dutch Catholic priest who left the church in 1536 and became an Anabaptist leader. His writings in many ways codified Anabaptist beliefs. Despite all Mennonites taking their name from this one figure, from the very beginning of the Mennonite faith, the movement was split between Dutch and Swiss-German groups, and later fragmented further still. Mennonites are pacifists, and are practitioners of the 3-fold Believer's Baptism: baptism by spirit, baptism by water and baptism by blood (martyrdom or ascetic lifestyle). Also, the Lord's Supper (Communion) is understood as a memorial instead of as a sacrament.
The Amish are the heirs of Jacob Amman, a reformer who tried to convince the larger German Mennonite faith to embrace certain changes. Among other things, he wanted to strengthen the discipline of the church to include excommunication and ostracism. This lead to a severe split in the Swiss Mennonite community in particular. It is widely believed that the Amish are anti-technology or regard it as sinful, which is a gross over-simplification and largely untrue. Instead, they have adopted certain practices in keeping with their communitarian values and to shun people from outside their community. The attitude of different Amish communities towards modern devices can vary markedly.
Coming to America
The Quakers were banished from New England and faced death if they dared to return, and were banned by law in the United Kingdom. William Penn established the colony of Pennsylvania in 1681 largely as a safe haven for Quakers. Penn began soliciting other persecuted Protestant groups to join the Quakers in his new colony, starting with the first German Mennonites settling in Germantown, Pennsylvania, in 1683. Roughly 100,000 Germans from the Palatinate region immigrated to Pennsylvania in the 18th Century, with about 3,000 of them being Mennonites and Amish.
All three faiths are alive and well in modern times. In 2006, there were almost 1.5 million practicing Mennonites. In 2008, there were about 225,000 Amish. No one knows exactly how many Quakers there are, but it is an international faith and their numbers were estimated at over 300,000 in 2007.