Answer:
Amish people are fundamentalist Mennonites, or Anabaptists.
In Lancaster County, Pa, there are many people of German or Dutch descent, called Pennsylvania Dutch. However, being Pennsylvania Dutch does NOT automatically make you Amish. The Amish may be of similar descent, but these terms are NOT mutually inclusive. The Amish are a religious group that make certain lifestyle choices, not a nationality.
As a result of the Holy Roman Empire, which engulfed Europe from the North Sea to the Mediterranean, Holland and Lorraine to Poland and Moravia, a large portion of "Germans," may actually be classified now with a more specific regional moniker. The Amish, founded by Jacob Amman in the latter 1600s, began emigration in the early 1800s as a result of religious persecution. Many "Dutch" emigrants came to America in the early 1800s, when the Holy Roman Empire still held a large amount of territory. It is accurate to call all of these people descendants of Germany, or Deutsch/ Dutch, since at the time, the place their ancestors lived was Germany, or Deutschland, but certainly not precise by modern geographical standards. Only a small percentage of these people are Amish, others may be Jews, Catholics, Quakers, Calvanists, etc.