After the fall of the Roman Empire in the 5th century, slavery persisted in Arab lands and in central Europe, where many Slavs were captured and taken as slaves to Germany (hence the derivation of the word). Historically, slave-owning societies included the Ottoman Empire, the Crimean khanate, the Inca Empire (Peru), and the Sokoto caliphate and the Hausa (Nigeria). Central Asians such as the Mongols, Kazakhs, and various Turkic groups also kept slaves, as did some Native American peoples (such as the Comanche and the Creek). In Spain and Portugal, where the reconquest of the peninsula from the Moors in the 15th century created an acute shortage of labor, captured Muslims were enslaved. Slaves soon followed them from Africa, imported by the Portuguese prince Henry the Navigator after 1444. Slaves were used for a wide range of tasks, and a regular trade in slaves was established between the Gulf of Guinea and the slave markets of the Iberian Peninsula.