[2][3] 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 for other organizational reasons.
[5][6][7][8] In the developing world, this model has been attractive in countries where Protestants are a small minority of the population; by pooling resources and endorsing cross-attendance between denominations, churches can serve a wider geographical area.
In the developed world, since the mid-20th century, and the rise of secularism worldwide, mainline Protestantism has shrunk, reducing the viability of many individual denominations maintaining parallel administrative structures.
[9][10][11][12] Among others, Reformed (Calvinist), Anglican, and Lutheran churches have merged, often creating large nationwide denominations.
The COCU disbanded formally in 2002 but moved into the Churches Uniting in Christ movement.