Islam began in the city of Mecca in Arabian Peninsula in 610 CE, 40 years after the Year of Elephant when Muhammad b. 'Abd Allah (s) was chosen as the prophet of Islam (a).The first period of Islam was the thirteen years of the Prophet's (a) life and preaching in Mecca. In this period, the Prophet (a) secretly invited people for three years. After three years, God ordered him to invite his close relatives to Islam. (See: Yawm al-Dar) In that period, few people accepted Islam. In years 12 and 13 after the beginning of his mission, the Prophet (a) provided the grounds for emigration to Yathrib by making two treaties of Bay'at al-'Aqaba.
In Rabi' al-Awwal, year 13 after the beginning of the mission, the Prophet (a) emigrated to Medina and with the people of Medina, established the first Islamic government. Companions of the Prophet (a) in Medina were in two big groups of Muhajirin [Emigrants] and Ansar [the Helpers]. Majority of the Helpers were from the two big tribes of Aws and Khazraj.In this period, the Prophet (a) was drawn to several battles which are recorded as Ghazawas and Sariyyas in the history. The most important Ghazawas of the Prophet (a) were the battles of Badr, Uhud, Khandaq and the Conquest of Mecca. After the Conquest of Mecca, almost all Arabian Peninsula became Muslim.In this period, the Prophet (a) wrote letters to the leaders of different countries and invited them to Islam. This period lasted ten years and entered a new era after the demise of the Prophet (a).
Period of the Three Caliphs
After the demise of the Prophet (a) in 11/632 in Medina, disregarding his will about the caliphate of Ali b. Abi Talib (a), some of his Companions chose Abu Bakr b. Abi Quhafa as the caliph. After Abu Bakr, 'Umar b. al-Khattab and then 'Uthman b. 'Affan became caliph.During the caliphate of the First Caliph, some clashes with disbelievers and some battles with false prophets have been reported. During the caliphate of the Second Caliph which lasted about ten years, Islamic territory was expanded and Muslims took over Iran, Syria, Egypt, and other places. During the caliphate of the Third Caliph, Islamic territory continued to be expanded. The most important event of that period was the civil revolts which led to the murder of the Third Caliph and the election of Ali b. Abi Talib (a) as the Fourth Caliph.
The Period of Imam Ali (a) and Imam al-Hasan (a)
The period of Imam Ali's (a) government (37/658 – 40) lasted less than five years. Three internal battles of Jamal, Siffin, and Nahrawan were among the most important events of this period. Imam Ali (a) was assassinated by one of Khawarij in the mosque of Kufa and people gave allegiance to his elder son, Imam al-Hasan (a).
The caliphate of Imam al-Hasan(a) lasted less than six months, most of which passed in the battle of Imam's (a) army with the army of Syria led by Mu'awiya b. Abi Sufyan. The battle ended by signing a peace treaty and leaving the caliphate to Mu'awiya.