Church union
Church union is the name given to a merger of two or more Christian denominations. Such unions may occur in one of two ways.
United churches
Some churches have formed as a result of a merger of churches of different denominations. One of the first of these occurred in 1817, when Lutheran and Reformed churches in Prussia merged in what is known as the Prussian Union.
The nineteenth century saw a number of unions between different churches of the same tradition. For example, the United Secession Church in Scotland was formed in 1820 by a union of various churches which had seceded from the established Church of Scotland. All these were Presbyterian in both doctrine and practice. In the twentieth century many churches merged as a result of the Ecumenical movement. One of the earliest such unions was in 1925, and formed the United Church of Canada.
Federation
Some churches may join together by way of federation.
On July 24, 1901, the Presbyterian Churches of New South Wales, Victoria, Queensland, South Australia, Tasmania and Western Australia joined together to form the Presbyterian Church of Australia. This was a federation, similar to the Federation which formed the Commonwealth of Australia on January 1 of that same year. In his inaugural moderatorial address, John Meiklejohn made it clear that the ecclesiastical union consciously reflected the union of the colonies: "We have, by forming this Assembly, formed a Court whose jurisdiction is, as regards territory, equal to, and coterminous with that of the Federal Parliament, and like it, is representative in its character."
This union involved churches of the same denomination in different locations. The individual state churches also kept their individual identities and retained many of their rights and privileges. A federal church rather than a national church was created.
The Uniates and the Edinovertsy
The term "union" (e.g., the Union of Brest of 1596) is also used for the arrangement whereby a particular group of Orthodox Christians enters communion with the Pope of Rome, while maintaining the Eastern rites. Such groups are known generically as Eastern Catholic Churches. Their adherents are occasionally referred to as uniates.
In a somewhat parallel way, but on a much smaller scale, Russian Orthodox Church has integrated certain Old Believer communities, allowing them to keep their rites while recognizing the authority of the national church. This arrangement is known as Edinoverie.