This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Reformed Christianity spread through the Low Countries under active persecution from Habsburg Spain, and its adherents first organised themselves not at home but in exile, at the Synod of Emden in October 1571, where twenty nine exiled Calvinist leaders gathered in the German town sheltering Dutch refugees. The synod adopted the 1561 Belgic Confession and set out a presbyterian structure of regional classes, an organisational skeleton built for a persecuted minority rather than an established church.
That skeleton is what the Dutch Reformed Church built on once the Revolt against Spain gave it room to grow, turning an exiles' framework into the Dutch Republic's own public church as Spanish control receded. The settlement was not left unchallenged from within: when the Arminian Remonstrants challenged Reformed orthodoxy on predestination, the Synod of Dort, meeting from November 1618 to May 1619 with delegates gathered from across Reformed Europe, ruled decisively against them and confirmed strict Calvinist doctrine as the Republic's own settled religious position.
What this changed for Christianity's spread was the transformation of a persecuted exile movement, meeting in a foreign town because it could not meet safely at home, into an entire nation's established church within half a century, then hardened by international debate rather than left to soften into ambiguity.