The main difference between Sunnis and Shias lies in their interpretation of the rightful succession of leadership after the death of the prophet Muhammad. The declaration of faith to which all Muslims assent is this: There is no God but Allah, whose prophet is Muhammad. However, the Shiites add an extra phrase at the end: and Ali is the friend of God. Because the Shiites passionately attest to Ali being the successor to Muhammad, much feuding and division have been caused in the world of Islam, not unlike the feuding between Protestants and Roman Catholics in Europe during the Reformation. However, the schism that sets up the major sects of Islam is not due to doctrinal issues, as between Protestants and Catholics, but is grounded in the identity of the “true successor” to Muhammad.