Since the early 1990s, Bin Laden has sought to purge the Islamic world of the influences that he believes have corrupted and degraded it. These influences, he believes, include American culture, U.S. military bases, the state of Israel, and the Arab governments who tolerate them. He likens Americans and Israelis to the European crusaders who seized Jerusalem from Muslim control in 1099 and were driven out by Arab armies in 1187. In 1998 bin Laden made explicit that killing Americans is the preferred means to achieve his goals.