United and uniting churches
Historically, unions of Protestant churches were enforced by the state, usually in order to have a stricter control over the religious sphere of its people, but also other organizational reasons. As modern Christian ecumenism progresses, unions between various Protestant traditions are becoming more and more common, resulting in a growing number of united and uniting churches. Some of the recent major examples are the Church of North India (1970), United Protestant Church of France (2013) and the Protestant Church in the Netherlands (2004). As mainline Protestantism shrinks in Europe and North America due to the rise of secularism, Reformed (Calvinist), Anglican and Lutheran denominations merge, often creating large nationwide denominations. The phenomenon is much less common among evangelical, nondenominational and charismatic churches as new ones arise and many of them remain independent of each other.
Perhaps the oldest official united church is found in Germany, where the Evangelical Church in Germany is a federation of Lutheran, United (Prussian Union) and Reformed churches, a union dating back to 1817. The first of the series of unions was at a synod in Idstein to form the Protestant Church in Hesse and Nassau in August 1817, commemorated in naming the church of Idstein Unionskirche one hundred years later.
Around the world, each united or uniting church comprises a different mix of predecessor Protestant denominations. Trends are visible, however, as most united and uniting churches have one or more predecessors with heritage in the Reformed tradition and many are members of the World Alliance of Reformed Churches.