The practice of raiding, both in war and peacetime, was a pastime of Bedouin warriors since ages.
Muhammad of Mecca used ghazis in the early battles of the Arab conquests, raiding caravans to and from Mecca.
Renamed akinji, they were also employed extensively by the Seljuk and Ottoman Turks against the Byzantine empire.
Several Ottoman emperors used 'Ghazi' as part of their throne name.
The purpose of the ghazis was to scout the enemy's frontiers and disrupt them by hurting him economically, demoralizing the population and causing chaos.
Islam avoided attacking civilians, though this did not include looting and destruction of property.
Ghazi raids preceded attacks by a regular army, which aimed at conquest rather than raiding.
Ghazis resembled mercenaries in their organization, which was loose and centered around successful leaders.
They were made up from adventurers, religious fanatics, political refugees and other people on the fringe of society.
Ghazi bands could form and dissolve fluidly.
They did not receive regular pay, but made a living from plunder.
Many Ottoman akinji fought fiercely in battles in order to distinguish themselves, hoping to be promoted into the regular army and receive fixed pay.
In peacetime, when the opportunities for raiding are low, many descended to ordinary brigandage.
In later centuries, other nations would use similar irregular troops, like the Slavic Cossacks and Greek klephts.
War Matrix - Ghazis
Islamic Age 630 CE - 800 CE, Armies and troops