Protestantism

===United and uniting churches===
{{Main|United and uniting churches}}
{{See also|Continuing churches}}
[[File:Union luthercalvin.jpg|thumb|upright=1.1|Glass window in the town church of [[Wiesloch]] featuring [[Martin Luther]] and [[John Calvin]] commemorating the 1821 union of [[Lutheranism|Lutheran]] and [[Calvinism|Reformed]] churches in the [[Grand Duchy of Baden]]]]
United and uniting churches are churches formed from the merger or other form of union of two or more different Protestant denominations.

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. 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]] or in areas where Christianity is a minority religion as with the [[Indian subcontinent]], [[Reformed church|Reformed]], [[Anglican]], and [[Lutheran]] denominations merge, often creating large nationwide denominations. The phenomenon is much less common among [[evangelical]], [[Nondenominational Christianity|nondenominational]] and [[charismatic]] churches as new ones arise and plenty of them remain independent of each other.{{Citation needed|date=October 2023}}

What is perhaps the oldest official united church is found in [[Germany]], where the [[Protestant Church in Germany]] is a federation of [[Lutheranism|Lutheran]], United ([[Prussian Union of churches|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, Idstein|Unionskirche]] one hundred years later.<ref>{{cite web |url=http://www.nassau-info.de/geschichte-jb-kirche.htm |title=Staatlicher Dirigismus und neue Gläubigkeit (Die Kirche im Herzogtum Nassau) |publisher=Nassau-info.de |language=de |access-date=27 May 2016 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303234050/http://www.nassau-info.de/geschichte-jb-kirche.htm |url-status=live }}</ref>

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 [[Calvinism|Reformed tradition]] and many are members of the [[World Alliance of Reformed Churches]].