Most historians cite the year 1095 A.D. as the start of the Crusades. This is generally accurate, but several qualifications must be added. First, the concept of a military counterattack into Islamic lands was indeed first proposed in 1095, but no concrete action was taken until 1096. Second, although the term 'Crusades' is usually used in the plural - historians identify variously six or nine or some other number of allegedly distinct Crusades - the counterattack begun in 1096 was arguably one long action. As scholar Harold Lamb writes,
historians have picked out six of the crises of this conflict and have named them the six crusades. In reality it was all just an ebb and flow of the conflict begun by
Islamic attacks against Europe as early as 711 A.D., when Muslims invaded Spain, almost four hundred years prior to the so-called Crusades. After decades of coastal raiding, Islamic armies invaded Italy in 841, and occupied portions of the Italian peninsula for several decades. Massive Muslim armies attempted to invade France in 732, but were repelled by the soldiers under the command of Charles "the Hammer" Martel. Repeat attempts to invade France over the following two centuries alternated with decades in which the Muslims were content to loot and pillage French coastal cities, but not permanently occupy them.
Third, an emphasis upon the concept of counterattack, i.e., a largely defensive maneuver, must be understood as central to the Crusades. Although the Islamic occupational armies were pushed out of Italy by 884, as historian Will Durant notes,
their raids continued, and central Italy lived through a generation of daily fear. In 876 they pillaged the Campagna; Rome was so endangered that the pope paid the Saracens a year bribe of 25,000 mancusi (c. $25,000) to keep the peace. In 884 they burned the great monastery of Monte Cassino to the ground; in sporadic attacks they ravaged the valley of the Anio; finally the combined forces of the pope, the Greek and German emperors, and the cities of southern and central Italy defeated them on the Garigliano (916), and a tragic century of invasion came to an end. Italy, perhaps Christianity, had had a narrow escape; had Rome fallen, the Saracens would have advanced upon Venice; and Venice taken, Constantinople would have been wedged in between two concentrations of Moslem power. On such chances of battle hung the theology of billions of men.
In 1095, Islamic armies still occupied Spain; Muslim raiders were still sacking coastal cities and island around the Mediterranean; Islamic pirates were still marauding among cargo ships in the Adriatic and Aegean. By 1095, Europe had endured almost 400 years of continuous attacks. The time to do something about it had arrived.