Congregational polity grew out of a specific complaint against the Church of England: that a national church governed by bishops answerable to the crown could not be the New Testament church, which the Separatists of the late sixteenth century read as a network of independent local assemblies, each one complete in itself under Christ. Robert Browne set out the position in print in 1582, arguing that a true church needed no bishop's permission to exist and no synod's permission to act, only a covenant among its own believing members.
The English Baptist congregations that formed in Amsterdam and London in the early 1600s inherited this conviction along with their doctrine of believer's baptism, and the two fit naturally together: a church made up only of professing, baptized adults was already, by definition, a gathered rather than an inherited membership, and a gathered membership was well suited to governing itself. Congregationalist churches proper, a separate but related tradition, carried the same principle of local self-government into New England in the 1620s and 1630s, most famously at Plymouth and the Massachusetts Bay Colony.
Both movements insisted that association among congregations, however valuable for fellowship or mission, must remain voluntary, since any body with binding authority over a local church would recreate the very hierarchy the Separatists had left.