Unio Trium Nationum

Unio Trium Nationum (Latin for "Union of the Three Nations") was a pact of mutual aid codified in 1438 by three Estates of Transylvania: the (largely Hungarian) nobility, the Saxon (German) burghers, and the free military Székelys. The union was directed against the peasantry, many of whom were Romanian Orthodox Christians, as a reaction to a widespread peasant rebellion.

In medieval times, Transylvania was organised into two types of territorial units:

With the rise of the Ottoman Empire, one of the first major Ottoman military campaigns against Transylvanian parts of the Kingdom of Hungary was organised in 1421. The invading forces entered the region from Wallachia. The Saxons and Székelys living in the border area tried to defend themselves, but were heavily outnumbered by the intruders. King Sigismund was not able to react promptly because he had recently inherited the Bohemian throne and was involved there in the Hussite Wars. Also, Transylvanian Diets had not been organized for decades and there was no forum to coordinate defence preparations of the three nations. Left alone, the Saxon Burzenland and the Székely Seat of Háromszék, both in the border region, were ravaged. Sigismund reacted to the attack only years later, leading a series of military campaigns against the Ottomans in Wallachia. The Ottomans, allied with the Wallachian Voivode, returned in 1432 and Southern Transylvania suffered serious damages again.

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