During the Reformation, the word Anabaptist was applied to Christians who rejected infant baptism in favor of baptizing only those old enough to profess faith in Jesus Christ for themselves. The term, which means re-baptizer, was not complimentary, just as the label Christian was used in a negative sense when it was first applied to Jesus’ disciples. At the time of the Reformation infant baptism was the norm not only in the Roman Catholic Church, but also in Protestant denominations that had split away. That meant that most people who wished to make a confession of faith and be baptized as adults had already been baptized as infants, so they had to be re-baptized.
At that time in Europe people weren’t given a choice as to which denomination to join. They were enrolled as members in the official church of their country at birth. If you were born in a Catholic country, you were a Catholic. If your country was Lutheran, then you were a Lutheran. Rejecting the prevailing church and becoming an Anabaptist led to serious persecution if not a death sentence. Many believers were formally expelled from their country or forced to flee, only to face persecution from the church holding sway in the country to which they fled.
During the 18th century, the continuing pressure of persecution in Europe led to the migration of many Anabaptists to the English colonies in North America, among them the Amish and Mennonites. Many members of these groups originally settled in Pennsylvania, where a large number of their communities are still located today.