parts of Greece established themselves along the Mediterranean coast of North Africa. They were later followed by colonists of the Roman Empire. Rome's colonies "served as a prototype" for later European colonial movement into the continent. Portugal was the first European empire to penetrate deep into Sub-Saharan Africa to establish colonies. Portuguese prince Henry the Navigator advanced Portuguese exploration of Africa, driven by two desires: to spread Christianity, and to establish Africa as a bastion of Christianity against the Ottoman Empire, which was making many African converts to Islam. Africa was exploited for commercial purposes because of another Portuguese goal: to find a route to India, which would open the entire Indian Ocean region to direct trade with Portugal. Conquest of territory in Africa also meant that the Portuguese could use African gold to finance travel along this new trade route. The Portuguese began significant trading with West Africa in the 15th century. This trade was primarily for the same commodities the Arabs had bought—gold, ivory, and slaves. The Portuguese sold the Africans Indian cloth and European manufactured goods but refused to sell them guns. Soon, however, other European powers such as France, Denmark, the Netherlands and Britain were developing their own trade with Africa, and they had fewer restrictions. The major European imperial powers in Africa were Portugal, Great Britain, France, and to a lesser extent Germany, Belgium, Spain and Italy. Portugal's presence in Africa as an imperial power lasted until the 1970s, when the last of its former colonies declared independence after years of war. The Atlantic Ocean had long been all but impenetrable to the galleys that plied the Mediterranean. That any ship needed to pass thousands of kilometers of waterless desert before reaching any populated regions also made trade impossible. These barriers were overcome by the development of the caravel in Europe. Previously, trade with Sub-Saharan Africa could only be conducted through North African middlemen. Now Europeans could trade directly with the Africans themselves. This valuable trade lead to rapid change in West Africa. The region had long been agriculturally productive and, especially in western Nigeria, densely populated. The massive profits from trade and the arrival of guns lead to significant centralization and a number of states formed in the region such as the Ashanti Confederacy and Kingdom of Benin. These states became some of the wealthiest and most advanced in Africa. Wealthy merchants began to