The territories of the 20 EKD member churches correspond in many cases to the borders of the kingdoms, dukedoms and principalities of the Napoleonic era and are a vestige of the much older cujus region, ejus religio principle, that is, "whose rule, their religion". The Federal Republic of Germany is comprised of 16 federal Länder or states. Their borders do not coincide with those of member churches.
Since the 19th century, there have been many efforts to consolidate the fellowship of regional churches. Collaboration among the regional churches began in 1852 with the Eisenach Conference of the German Evangelical Church; it continued with the founding of the Federation of German Evangelical Churches in 1922. In 1933, after the National Socialists came to power, a Reich law was passed creating the German Evangelical Church (DEK), an attempt to institute a state church within a church-hostile state. The DEK was supported by German Christians who were close to the NSDAP, the Nazi party. This attempt by the dictatorship to embrace the church met with the resistance of the Confessing Church. Following the war, in 1948, the German regional churches adopted a constitution and formed the Evangelical Church in Germany (EKD). A fellowship of Lutheran, Reformed and United churches, the EKD is a public-law corporation, as are its member churches.
Participation in the EKD by the regional churches in East Germany was increasingly obstructed by the East German regime. As a result, with the protection they enjoyed by virtue of their "special fellowship" with the regional churches of the West, they formed in 1969 the Federation of Evangelical Churches in the GDR (BEK), thus safeguarding the independence and democratic structure of their governing bodies. These churches provided a safe haven for open discussions and in that way, contributed to the peaceful political transition. After the reunification of East and West Germany in 1990, the BEK was dissolved and member churches from the East took over their dormant rights within the EKD.
Because of doctrinal differences which at the time of the EKD's creation in 1948 were still a source of division between Lutheran, Reformed and United churches and in order to preserve Lutheran identity, eight Lutheran regional churches joined together to form the United Evangelical Lutheran Church of Germany (VELKD). Unlike the VELKD, the Reformed Alliance considers itself to be an umbrella association whose membership includes two Reformed churches which are also members of the EKD. In 1967, EKD member churches that are not part of the VELKD (with the exception of Evangelical Church in Württemberg, which has guest status) formed the Arnoldshain Conference (AKf), a working association of church governing bodies.
The Evangelical Church of the Union (EKU) replaced the Old Prussian Union and is made up of the seven United regional churches located in the area that was formerly Prussia. In 2003, EKU and AKf churches joined together to form the Union of Evangelical Churches within the EKD (UEK), to which 13 regional churches belong (in addition to the Evangelical Church in Württemberg and the Evangelical Lutheran Church in Oldenburg, who have guest status).
In 2005, the EKD, VELKD and UEK sealed an agreement to greatly strengthen their collaboration.