The history of military of the Ottoman Empire can be divided in five main periods. The foundation era covers the years between 1300 (Byzantine expedition) and 1453 (Fall of Constantinople), the classical period covers the years between 1451 (enthronement of Sultan Mehmed II) and 1606 (Peace of Zsitvatorok), the reformation period covers the years between 1606 and 1826 (Vaka-i Hayriye), the modernisation period covers the years between 1826 and 1858 and decline period covers the years between 1861 (enthronement of Sultan Abdülaziz) and 1918 (Armistice of Mudros).
The earliest form of the Ottoman military was a steppe-nomadic cavalry force. This was centralized by Osman I from Turkoman tribesmen inhabiting western Anatolia in the late 13th century.
These horsemen became an irregular force of raiders used as shock troops, armed with simple weapons like bows and spears. They were given fiefs called timars in the conquered lands, and were later called timariots. In addition they acquired wealth during campaigns.
Orhan I organized a standing army paid by salary rather than booty or fiefs. The infantry were called yayas and the cavalry was known as müsellems. The force was made up by foreign mercenaries for the most part, and only a few Turks were content to accept salaries in place of timars. Foreign mercenaries were not required to convert to Islam as long as they obeyed their Ottoman commanders.
The Ottomans began using guns sometime at the 15th century. Following that, other troop types began to appear, such as the regular musketeers (Piyade Topçu, literally "foot artillery"); regular cavalry armed with firearms (Süvari Topçu Neferi, literally "mounted artillery soldier"), similar to the later European reiter or carabinier; and bombardiers (Humbaracı), consisting of grenadiers who threw explosives called khımbara and the soldiers who served the artillery with maintenance and powder supplies.