In the late 1500's, the Ottoman Empire started going into decline as a result of both internal and external factors. Internally, the Ottomans suffered from less capable sultans after Suleiman's death who began wasting their time at court. This spawned massive corruption that spread across their large difficult to manage empire while the Janissaries became a virtual hereditary caste demanding increasingly more pay while growing soft and lazy.
After 1600, the Turks lost their technological and military edge and stagnated while their line of expensive fortresses drained the empire of even more money. Without wars of conquest to enrich them, the Turks became restless and troublesome to the central government. That combined with the problems from the Janissaries caused revolts that further disrupted the empire.
The following centuries saw the Ottoman Empire suffer from steady political and economic decay. By the 1800's, its decrepit condition would earn it the uncomplimentary title of "The Sick Man of Europe".
Finally, the shock of World War I would destroy the Ottoman Empire once and for all and the Triple Entente (e.g. Russia, France, and Britain supplemented by agreements with Portugal and Japan) broke it into the respective nations we have today.