If we define Islam, not as the practice of Muslims, but as the teachings of Muhammad then violence is an integral part of Islam.
Those Muslims who teach that surah 9 of the Quran has not been abrogated (the final teaching of Muhammad), still affirm the command to disavow all treaties with polytheists and to subjugate Jews and Christians so that Islam may "prevail over every faith." This final surah of the Quran gives no limits to assimilation, subjugation and violence against non-Muslims. According to this surah those Muslims who do not fight are even counted among the hypocrites.
Former Muslim Nabeel Qureshi says,
"...frustrated by the increasing frequency and scale of Islamist terrorism [many people] suggest that Islam needs a reformation. What they may not realize is that radical Islam is the Islamic Reformation.
This might sound shocking, but consider: Just as the Protestant Reformation was an attempt to raze centuries of Catholic tradition and return to the canonical texts, so radical Islam is an attempt to raze centuries of traditions of various schools of Islamic thought and return to the canonical texts of the Quran and Muhammad's life.
The question arises then, If Muhammad taught this, why don't all Muslims believe this then? Because each persons Islam is interpreted through the tradition of their local imam or jurist. Many local imams may claim this part of the Quran has been abrogated. But those Muslims who continue to affirm surah 9 and the traditions of Muhammad and the earliest followers of Muhammad, believe violence or subjugation against non- Muslims is still valid. Qureshi says,