by caliph 'Umar ibn al-Khattab. The imposition of tribute upon the conquered Jews served as a precedent for provisions in the Islamic law for the jizya. Byzantine campaign In the final years of his life, after suppressing the two main factions that were leading in the opposition against him; the Meccans and the Jews, Muhammad led an active campaign against the main force in the north, the Byzantine Empire, which was involved in several wars against the Sasanian Empire, known as the Roman–Persian Wars. Following a defeat in the Battle of Mu'tah in Muhammad's campaign against the Byzantine began with the final expedition led by Muhammad himself, the Tabuk expedition, which is also known as the Usra expedition. Muhammad heard of the gathering of a large Byzantine–Ghassanid alliance against the Muslims in Tabuk and led a force of some 30,000 men to look for them. After waiting and scouting for the enemy for twenty days, Muhammad returned to Medina. Statistics The number of all casualties on all sides, in all the battles of Muhammad, is approximately 1,000. A contemporary Islamic scholar, Maulana Wahiduddin Khan, says that "during the 23-years in which this revolution was completed, 80 military expeditions took place. Fewer than 20 expeditions actually involved any fighting. 259 Muslims and 759 non-Muslims died in these battles – a total of 1018 dead." Most of those killed were men from the Banu Qurayza tribe after they surrendered to a siege as an aftermath of the Invasion of Banu Qurayza. Legacy Javed Ahmed Ghamidi writes in Mizan that there are certain directives of the Qur’an pertaining to war which were specific only to Muhammad against divinely-specified peoples of his times (the polytheists and the Israelites and Nazarites of Arabia and some other Jews, Christians, et al.) as a form of divine punishment—for they had persistently denied the truth of Muhammad's mission even after it had been made conclusively evident to them by Allah through Muhammad, and asked the polytheists of Arabia for submission to Islam as a condition for exoneration and the others for jizya and submission to the political authority of the Muslims for military protection as the dhimmis of the Muslims. Therefore, after Muhammad and his companions, there is no concept in Islam obliging Muslims to wage war for propagation or implementation of Islam, hence now, the only valid reason for war is to end oppression when all other