Qutbism is a theory of Islamism that was developed by Sayyid Qutb, the figurehead of the Muslim Brotherhood, during the 1950s and 1960s. Qutb's views were shaped by his experiences in the United States from 1948 to 1950, during which time he had lived in Greeley, Colorado and New York City. Qutb argued that morality could only be enforced through sharia law; that sharia would bring justice, peace, personal security, scientific discovery, freedom from servitude, and other benefits; avoidance of Western and non-Islamic cultural corruption such as socialism, nationalism, and capitalism; vigilance against Western and "Jewish" conspiracies against Islam, preaching to convert and jihad to forcibly eliminate structures of jahiliyya (pre-Islamic culture in the Arab World); and the importance of jihad to eliminate jahiliyya from the face of the Earth. Qutb was also a revolutionary, believing in vanguardism and the violent overthrow of the Nasserist regime that ruled Egypt during the 1950s and 1960s. He was executed in 1966 for attempting to assassinate Gamal Abdel Nasser, but his ideology became popular among the youths who had studied at Brotherhood-run mosques. His most important disciple was Ayman al-Zawahiri, who led his vanguard movement as the "Egyptian Islamic Jihad" movement, and who would serve as mentor and successor to al-Qaeda founder Osama Bin Laden. Both traditionalist and Salafist Muslims found points to criticize in Qutb's works, including his socialistic proposals to redistribute income and property to the needy, his opposition to slavery, his desire to unite the four schools of Islam into one school, and his favoring of the overthrow of tyrants.