Prior to 1801, Congregationalists and Presbyterians had enjoyed friendly relationships. Both denominations shared a common Calvinistic theology, while differing in church polity. There were also many instances stretching back to colonial times where Puritan congregations embraced presbyterian polity.
Provisions
The Plan of Union was initially agreed upon between the General Assembly of the Presbyterian Church and the Connecticut General Association of Congregational Churches. The Plan was later approved by the Congregational associations in Vermont, New Hampshire, and Massachusetts. It enabled churches of either denomination to hire ministers from the other. Congregations were given the choice whether to be governed by congregational polity or by the Presbyterian model of a session of ruling elders. The Plan also made it possible for the Middle Association of Congregationalists in New York to become a subordinate jurisdiction of the Presbyterian Synod of Albany. As part of the Plan, the General Assembly of the Presbyterian Church designated the Congregationalist American Board of Commissioners for Foreign Missions as its recognized missions agency in 1826. By 1831, the majority of board members and missionaries of the ABCFM were Presbyterians. As a result, most of the local churches established by the organization during this period were Presbyterian. Congregationalists essentially "turned over domestic evangelistic efforts to Presbyterians".
Termination
A consequence of this arrangement was that the Presbyterian Church received an influx of pastors and congregations sympathetic to the New England theology that prevailed within the Congregational churches. This ultimately led to the Old School-New School Controversy that divided the Presbyterian Church in 1837. The Old School Presbyterian Church ended cooperation with the Congregationalists in 1837, but the New School Presbyterian Church would remain in union with the Congregational churches until 1852. That year the Congregationalists ended their participation in the Plan of Union. By this time, Congregationalists had developed a greater denominational consciousness, which ultimately led to the creation of the National Council of the Congregational Churches in 1865.
