The War of the Hijaz was an internal religious conflict located within tribal Hijaz in the early and mid-VII Century. The war was started after the leader of the small Medinan community's leader, Muhammad, was assassinated by a Quaraysh-hired assassin. The Muslim community, forced to flee to Mecca, thus declared war on the Quaraysh.
Muhammad begun preaching his version of Christianity in the year 610 after getting a "illumination" from God that told him the "true branch of Christianity". He was able to get a small community of followers (numbering 650 by 615 AD). However, this angered the Quraysh community, who felt the Medinan congregation was a threat to them.
The pagan Quaraysh had enough and in 615, sent an assassin to murder Muhammad. The assassin, successful, infuriated and scared the Christian community. They (now led by Fatimah I, Muhammad's daughter) were forced to flee northeast to the town of Yathrib, which from then on would be named Medina (litteraly "the city").
In Medina, the Christian (from then on mostly known as Medinan) community received huge support from a wealthy faction in the city; the Jewish community. They gave support and refuge to the Medinan faction, who gained a lot of converts among the local Pagan Banu Aus and Khazraj (Later on, in return for the help given to the Jews, the Jews were put in rule over Medina as soon as the Medinan community marched south). They soon were attacked, in Medina,by a large joint Pagan Quaraysh, Hawazan and Banu Aus army. However, the Medinans, with a larger knowledge of the area and a brilliant leadership, were able to defeat the Pagans.
The Medinans then marched south, occupying cities and placing either converts or Christians into office. At last, they reached a city which opposed them to a point; a second Pagan army met the Medinans in the city. While this time, the Medinan host (now greatly strengthened) received major losses and was the one without knowing of the territory, they at last won, killing the major generals in the battle.
From then on, Pagan morale broke. The Medinans found it increasingly easy to cross over to Mecca, which they seized and marched through gloriously.
The last pockets of resistance were destroyed in the Battle of Jiddah in 631.
The war ended into a glorious Medinan victory, with the whole Hijaz becoming de jure Medinan (although most tribes remained Pagan). It also left, for the first time in recorded history, a unified, independent and ethnically Arabian power within the heart of the Peninsula.
The surprising fighting strength and zealous conviction of the Medinans caused them to overcome Arabian soldiers easily. This boost to Arabian morale would later lead the Arabian army to shortly become the best-trained in the world (it started decline after the First Arabian War and entirely lost its title by the second one). This caused Hijaz (and later on, the Medinan Empire as a whole) to enter the diplomatic stage, for the first time causing an important local Arabian power in the world.
Culturally, the war ravaged the countryside in no small part, leading many bedouins and small farmers to leave for towns and cities, or found their own. This is among the first attempted large-scale urbanisation attempts since the Roman Empire, and would lead to the end of the great tribal power in favour of a more "normal" semi-centralised monarchy. It also begun spreading Arabic as the language of the area, especially in areas where local dialects were spoken.