Following the Ottoman's defeat in the war, their Empire was split into several smaller countries. The heartland of the Empire became which modern nation?

At its height the Ottoman Empire covered a vast area, from modern day Hungary in the north, Iran in the east, Saudi Arabia in the south and Algeria in the west.  The Ottomans joined the war on the side of Germany, hoping to regain lands they had lost to Russia 40 years earlier.  It turned out to be a disastrous move and after the war the Ottoman Empire, which had lasted for more than 600 years, was no more.