Hungary was Christianised from the west by Stephen I, crowned in the year 1000 with a crown sent from Rome, and the Holy Crown itself went on to acquire a legal personality in Hungarian constitutional theory that no other regalia has held: sovereignty was said to reside in the crown rather than in the person wearing it.
The Reformation then divided the country along a line that still shows. Calvinism took hold east of the Danube and in Transylvania so firmly that Debrecen was known as the Calvinist Rome, while the Habsburg controlled west and north stayed Catholic and was worked over thoroughly by the Counter Reformation. Roughly speaking, the Catholic majority and the Reformed minority of today are the residue of that settlement, though affiliation has fallen sharply and a large share of Hungarians now decline to state one.
Transylvania produced something remarkable in the middle of it. The Edict of Torda, issued by the diet in 1568 under the Unitarian influenced prince John Sigismund, granted freedom of preaching and forbade the punishment of ministers for their teaching, recognising four received religions: Catholic, Lutheran, Calvinist and Unitarian. It is among the earliest acts of legal religious toleration in Europe, and Transylvania is where organised Unitarianism has its oldest continuous institutional life.
The twentieth century produced the emblematic figure of church resistance in Cardinal Jozsef Mindszenty, tortured and imprisoned by the communist government, freed during the 1956 revolution and then resident inside the United States embassy in Budapest for fifteen years, unable to leave without arrest.