Religious persecution drove the Brethren to take refuge in Surhuisterveen, Friesland, in the Netherlands. They settled among the Mennonites and remained there until 1729. Eventually all but a handful emigrated to America in three separate groups between 1719 and 1733. Because of growing persecution and economic hardship, Brethren began emigrating to Pennsylvania under the leadership of Peter Becker. Most Brethren left Europe by 1740, including Mack, who brought a group over in 1729. The first congregation in the New World was organized at Germantown, Pa., in 1723. Soon after its formation, the Germantown congregation sent missionaries to rural areas around Philadelphia. These missionaries preached, baptized, and started new congregations.