The Ottoman Empire's power and prestige peaked in the 16th and 17th centuries, particularly during the reign of Suleiman the Magnificent. The empire was often at odds with the Holy Roman Empire in its steady advance towards Central Europe through the Balkans and the southern part of the Polish-Lithuanian Commonwealth. At sea, the empire contended with the Holy Leagues, composed of Habsburg Spain, the Republic of Venice and the Knights of St. John, for control of the Mediterranean. In the Indian Ocean, the Ottoman navy frequently confronted Portuguese fleets in order to defend its traditional monopoly over the maritime trade routes between East Asia and Western Europe; these routes faced new competition with the Portuguese discovery of the Cape of Good Hope in 1488. In addition, the Ottomans were occasionally at war with Persia over territorial disputes or caused by religious differences between 16th and 18th centuries. During nearly two centuries of decline, the Ottoman Empire gradually shrank in size, military power, and wealth. It entered World War I on the side of the Central Powers and was ultimately defeated.