The Ottoman Turks, after staving off Timur, proceeded to conquer the Golden Horde. Despite garrisoning all fortresses and having roving armies to put down rebellions, all the world still considered the Golden Horde a legitimate existent (if occupied) country 150 years later- with the Ottomans at war with them. Multiple German-Catholic city-states, feeling that the Ottomans must be totally preoccupied
rolleyes
with war with the Horde, declared a Holy War on the Empire; despite the presence of an army 10 times the size of theirs standing on the frontier. This they did without a single ally in the world. After losing their army quickly, their 2000-man garrison felt confident enough to ask the Ottoman general of 22,000 for peace: "Tell you what, kind sir, if you just give us all the money your country has, and, while your at it, cede land to create a Greek country (or maybe two, depends on how merciful we feel), we'll let you and your army walk away". The sheer audacity of the offer led to the slaughter of the entire garrison, and the annexation of the city-state. At which point another German city-state felt it was their duty to do
the exact same thing.
Despite being militarily and technologically superior to their Christian enemies to the west, the Ottomans knew that these Christian nations had superior methods of research and strived to emulate them.
and
The Holy Roman Emperor, after much deliberation, decided the best possible way of unifying a German-Italian Catholic HRE under his hand was to convert to a religion which differed from everyone else's.