It is this border which is reflected in Huntington’s ‘Clash of Civilizations’ theory.

Middle era

The Ottomans fell behind the Europeans in military technology as the Empire became stifled by religious and intellectual conservatism. Changes in European military tactics and weaponry caused the once-feared Sipahi cavalry to lose military relevance. With the Empire's population reaching 30,000,000 people by 1600, shortage of land placed further pressure on the government.

However, the Ottoman state adapted to new pressures and realities, internal and external. The Sultanate of women (1648–1656) was a period in which the political influence of the Imperial Harem was dominant, as the mothers of young sultans exercised power on behalf of their sons.

This period gave way to the Köprülü Era (1656–1703), when imperial control was exercised by Grand Viziers, but came to a calamitous end when Grand Vizier Kara Mustafa Pasha in May 1683 attempted a second siege of Vienna. His final assault was delayed, so the Ottoman forces were swept away by allied Habsburg, German and Polish forces.

For the first time, the Ottoman Empire surrendered control of significant European territories (many permanently), including Hungary. The Empire had reached the end of its ability to effectively conduct an assertive, expansionist policy against its European rivals and it was to be forced from this point to adopt an essentially defensive strategy within this theatre.

Threats to the Ottoman Empire were presented by the traditional foe—the Austrian Empire—as well as by a new foe—the rising Russian Empire. The Ottoman Turks ceded much territory in the Balkans to Austria. Certain areas, such as Egypt and Algeria, became independent in all but name. By the 18th century, centralized authority within the Ottoman Empire gave way to varying degrees of provincial autonomy under local governors.

Following the Treaty of Belgrade in 1739, the Ottoman Empire enjoyed a generation of peace as Austria and Russia turned to the Prussian threat. This long period of peace had educational and technological reforms, such as starting Istanbul Technical University. Science and technology had long been highly regarded, as a result of scholars' synthesis of classical learning with Islamic philosophy and mathematics, and knowledge of such Chinese advances as gunpowder and the magnetic compass. But now the rulers were conservative. When an artillery school was set up with French teachers to impart Western-style methods, the Islamic clergy successfully objected. Not until 1754 was the artillery school re-opened on a semi-secret basis. Also, the writers’ guilds denounced Gutenberg’s printing press as "the Devil's Invention". It was used only by non-Muslims for over fifty years.

Russia began to expand again in 1768. Many defeats led Sultan Selim to conclude that Russian reforms of "Deli Petro" had given the Russians an edge, and the Ottomans would have to keep up with Western technology. But efforts were hampered by reactionary movements, primarily from the Janissary corps. Jealous of their privileges and opposed to change, they revolted. Selim's efforts cost him his throne and his life.