The term Salafi actually refers to 'Salaf' (the pious predecessors, that is the first 3 generations of Islam, collectively).
They, including Mohammad himself, exercised a great deal of brutality to gain terrain, convert people to Islam as well as raided caravans for economic reasons.
Same tactics are employed by ISIS, which work towards their stated objective of establishing an Islamic Caliphate.
The same conditions are in effect. The Roman Empire had collapsed so there was no great power, and there was division between the Eastern and Western Church with the result that institutional Christianity was weak.
Islam was a bizarre syncretist heresy dreamed up by its founder, who was a member of a primitive caravan raiding tribe of Arabs, to justify his behavior and also to subdue the populace of the places he attacked.