The Rashidun army () was the core of the Rashidun Caliphate's armed forces during the early Muslim conquests in the 7th century. The army is reported to have maintained a high level of discipline, strategic prowess and organization, granting them successive victories in their various campaigns.
In its time, the Rashidun army was a very powerful and effective force. The three most successful generals of the army were Khalid ibn al-Walid, who conquered Persian Mesopotamia and the Roman Levant, Abu Ubaidah ibn al-Jarrah, who also conquered parts of the Roman Levant, and Amr ibn al-As, who conquered Roman Egypt. The army was a key component in the Rashidun Caliphate's territorial expansion and served as a medium for the early spread of Islam into the territories it conquered.
Historical overview
According to Tarikh at Tabari, the nucleus of the early caliphate forces were formed from the Green Division (al-Katibah al-Khadra), a unit that consisted of early converts from Muhajirun and Ansar that marched on to conquer Mecca.
Ridda wars
Upon Muhammad's death, the Muslim community was unprepared for the loss of its leader and many experienced a profound shock. Umar was particularly affected, instead declaring that Muhammad had gone to consult with God and would soon return, threatening anyone who would say that Muhammad was dead. Abu Bakr, having returned to Medina, calmed Umar by showing him Muhammad's body, convincing him of his death. He then addressed those who had gathered at the mosque, saying, "If anyone worships Muhammad, Muhammad is dead. If anyone worships God, God is alive, immortal", thus putting an end to any idolising impulse in the population. He then concluded with a verse from the Quran: "Muhammad is no more than an apostle, and many apostles have passed away before him."
Troubles emerged soon after Abu Bakr's succession, with several Arab tribes launching revolts, threatening the unity and stability of the new community and state. These insurgencies and the caliphate's responses to them are collectively referred to as the Ridda wars ("Wars of Apostasy").
The opposition movements came in two forms. One type challenged the political power of the nascent caliphate as well as the religious authority of Islam with the acclamation of rival ideologies, headed by political leaders who claimed the mantle of prophethood in the manner that Muhammad had done. These rebellions include: that of the Banu Asad ibn Khuzaymah headed by Tulayha ibn Khuwaylid that of the Banu Hanifa headed by Musaylimah those from among the Banu Taghlib and the Bani Tamim headed by Sajah that of the Al-Ansi headed by Al-Aswad Al-Ansi Omani rebels led by Laqeet bin Malik These leaders are all denounced in Islamic histories as "false prophets".
The second form of opposition movement was more strictly political in character. Some of the revolts of this type took the form of tax rebellions in Najd among tribes such as the Banu Fazara and Banu Tamim. Other dissenters, while initially allied with the Muslims, used Muhammad's death as an opportunity to attempt to restrict the growth of the new Islamic state. They include some of the Rabīʿa in Bahrayn, the Azd in Oman, as well as among the Kinda and Khawlan in Yemen.
At their heart, the Ridda movements were challenges to the political and religious supremacy of the Islamic state. Through his success in suppressing the insurrections, Abu Bakr had in effect continued the political consolidation which had begun under Muhammad's leadership with relatively little interruption. By the wars' end, he had established Islamic hegemony over the entire Arabian Peninsula.
Military expansions
After the Treaty of Hudaybiyyah in 628, Islamic tradition holds that Muhammad sent many letters to the princes, kings, and chiefs of the various tribes and kingdoms of the time, exhorting them to convert to Islam and bow to the order of God. These letters were carried by ambassadors to Persia, Byzantium, Ethiopia, Egypt, Yemen, and Hira (Iraq) on the same day. This assertion has been brought under scrutiny by some modern historians of Islam—notably Grimme and Caetani. Particularly in dispute is the assertion that Khosrau II received a letter from Muhammad, as the Sassanid court ceremony was notoriously intricate, and it is unlikely that a letter from what at the time was a minor regional power would have reached the hands of the Shahanshah.
With regards to Persia, Muslim histories further recount that at the beginning of the seventh year of migration, Muhammad appointed one of his officers, Abdullah Huzafah Sahmi Qarashi, to carry his letter to Khosrau II inviting him to convert: