UNIONE (PROTESTANTE). — Defensive league concluded in Bavarian Swabia on 16 May 1608 between the representative of the Elector Palatine Cristiano di Anhalt, the duke of Württemberg, and the margraves of Ansbach, Kulmbach, Baden-Durlach, and Neuburg, initially for ten years, subsequently extended in 1617 for a further three. In 1609 the free cities of Strasbourg, Ulm, and Nuremberg joined it; in 1610, the Elector of Brandenburg, the margrave of Hesse-Kassel, and numerous other cities.
The U., under the presidency of Elector Palatine Federico IV, immediately sought to conclude secret agreements with foreign princes who were enemies of the House of Habsburg, interested in preventing the strengthening of the principle of unity in Germany, or supporters of the Protestant cause; it thus succeeded in opening negotiations with France, which nevertheless suffered a crisis following the death of Enrico IV; it established formal agreements with England (1612) and the Netherlands (1613); and it secured at least the benevolent support of Sweden and Denmark. The occasion that gave rise to the U., to which the Catholic side opposed the Catholic League as early as 1609, was a dispute that arose at Donauwörth over the interpretation of the Peace of Augsburg of 1555; in reality, the Protestants intended to establish a united front against the religious and political Catholic revival, which threatened the more or less regular possession of secularized territories and goods, and which also sought to exploit the doctrinal and political-territorial divergences between Calvinists and Lutherans. It thus became the center of all anti-Catholic and anti-Habsburg intrigues and, in this capacity, intervened in the question of the succession to the Duchy of Jülich in favor of the Protestant claimant (1609–10), and created the atmosphere for the Bohemian insurrection that initiated the political-religious Thirty Years’ War. Following the defeat of the insurgents in the battle of White Mountain, after initially making peace with the Catholic League, it dissolved in May 1621, only to re-emerge later in another form, at the prompting of Richelieu’s anti-Habsburg policy.