If history had been different, the most unlikely event of diplomatic history, ie. the Ottoman Empire leading a Balkan bloc (Greece, Albania, Yugoslavia, Bulgaria and Romania).
It came through the genius and sheer determination of Ioannis Metaxas and Mustafa Kemal, who met while fighting in 1917 and become best friends.
At first, Balkan nations all hated the Turks as well as each other. But then, Austria and Hungary, that had been turned into independent republics by the victorious Entente, re-united into Austria-Hungary.
Then, the Triple Alliance was reborn, with Austrians and Hungarians wanting to control Romania, Italians wanting Greece and Albania, both planning to carve Yugoslavia, and Germans supporting those plans.
The Triple Alliance also had grandiose plans about re-establishing the Kingdom of Jerusalem (under Habsburg Crown) with European colonists, while Italians saw themselves in Cairo and Suez, and Germans in Crete and Cyprus.
Of course, it all comes down to the Revivalism, a white supremacist and Christian ideology, that said Germany, Austria and Hungary lost because théy were allied with a Muslim power and tolerated Jews (a "cursed race") at home.
The answer was to re-unite the Balkans under their protection (and purge them of Pomaks, Jews, Gypsies...), as well as carving their Lebensraum out of Ottoman territory.
The Balkan Pact was the answer to this silliness...
Not only that, but with its oil and other resources, the Ottomans weathered the Depression decently. And the customs union with the Empire indeed revitalized Balkan economies.