The great fracture in Scottish church history was about who chooses a minister. Patronage gave the right of presentation to a landowner, and evangelicals in the church held that a congregation must be able to refuse. Ten years of litigation followed, in which the civil courts ruled that the church could not set aside a patron presentation, and the church replied that the courts had no jurisdiction over its spiritual acts.
In 1843 that argument ended in the Disruption. About a third of the ministry walked out of the General Assembly, gave up their manses, their stipends and their churches, and constituted the Free Church of Scotland. It was the largest voluntary surrender of livelihood in the history of any British church, and it left Scotland with two large Presbyterian bodies where there had been one.
Reunion took most of a century and required the state to move. The Church of Scotland Act of 1921 recognised the Articles Declaratory, in which the church states that it holds its spiritual jurisdiction directly from Christ and not from parliament, and that no civil authority may determine what it teaches or who it ordains. Parliament acknowledged the claim rather than granting it, which is the distinction the church cares about. With that settled, most of the Free Church tradition reunited with the national church in 1929. A continuing Free Church, and other bodies formed at other partings, remain separate.