Most historians of the Ottoman Empire will argue that the conquest of Constantinople by Sultan Mehmet II was the important victory that Ottomans ever won.

Beginning in 1699, the loss of Hungary to Austria was a blow to the Ottoman Empire. Over the next two hundred years, territorial disintegration slowly continued. Also, the rise of nationalism among nations under Ottoman rule, caused serious problems for the Ottoman's.

The Ottoman Empire was populated by the

You do not specify which eastern empire you are referring to. If you mean the Byzantine Empire, which is a term used by historians to refer to the eastern part of the Roman Empire after the fall of its western part, it fell in 1453, when the Ottoman Turks captured its capital, Constantinople.

The Ottoman Empire was a nation.