Crusade of Varna

The Crusade of Varna was a military conflict launched by Christians to push the Ottomans out of Europe. In real history, the Ottoman victory at the Battle of Varna marked the failure of the crusade, but Brazilian's Varna series is based on the premise that the battle was an Ottoman defeat. 
In the Varna series, the Ottomans stood alone against the following states:
* The State of the Church
* Kingdom of Poland
** Grand Duchy of Lithuania
** Kingdom of Hungary
*** Kingdom of Croatia
* Archduchy of Austria
** Holy Roman Empire
** Kingdom of Bohemia
* The Teutonic Order
* Despotate of Serbia
* Kingdom of Bosnia
* Principality of Wallachia
* Bulgarian rebel forces
* Byzantium and other Anatolian Greeks
With naval assistance from:
* Most Serene Republic of Venice
* Republic of Ragusa
* Duchy of Burgundy
And external intervention from:
* Mamluk Sultanate
* Beylik of Karaman (which later became the Sultanate of Rum)
The Ottoman Empire was written out of existence by the Treaty of Constantinople.