During this period in the 15th and 16th centuries, the Ottoman Empire entered a long period of conquest and expansion, extending its borders deep into Europe and North Africa. Conquests on land were driven by the discipline and innovation of the Ottoman military; and on the sea, the Ottoman Navy aided this expansion significantly. The navy also contested and protected key seagoing trade routes, in competition with the Italian city states in the Black, Aegean and Mediterranean seas and the Portuguese in the Red Sea and Indian Ocean.