The Arabs, after Prophet's death, conquered a large part of the world. What was the motivation behind this?

Political expansion and religious expansion are two different things. There is no proof that sword was used to spread Islam. However, there existed dynasties which in order to fulfill their political ambitions conquered newer lands but there is no proof that people were made to accept Islam per force. Swami Vivekananda wrote in his book, “Letters of Vivekananda,” “It is nonsense to say that Hindus were converted to Islam by force.” Similarly Egypt was a large country to enter within the fold of Islam. Sir Arthur Keith, while studying

the phenomenon remarked, “Egyptians were conquered not by sword but by Quran.” History does not prove that sword was used for religious expansion of Islam. Political expansion was a different case, specific to individuals and dynasties.