The Ottomans conquered the Byzantine Empire, in present-day Turkey and Greece, and formed one of the longest-lived empires in history, lasting until World War I. The Ottomans became one of the richest nations on Earth due to trade. They were among the first nations to use cannons and muskets in the 1400s and formed an empire that included Egypt, Iraq, North Africa, Arabia, and Greece. They challenged the other great powers of Europe for centuries and defined the Muslim world. However, by the 1900s, they were known as the 'sick man of Europe.' A long series of wars, inefficient governance and demoralized people had led them to become a shadow of their former self. When World War I kicked off, they sided with Austria and Germany, as they needed a European ally and none of the other nations wanted to ally with them.
They wound up losing big in WWI, as Britain and France partitioned the Ottoman Empire in a treaty known as the Sykes-Picot Agreement. Territories that were cut off from the Ottoman Empire (which became Turkey) after WWI include Greece, Syria, Iraq, Egypt, Israel, Saudi Arabia, and several others. The British and French did this to establish Middle-Eastern colonies but abandoned the region after WWII. A hundred years later, the Middle East is still unstable, partially because of the partition.