Far more controversial than what occurred at Tours is the effect of the battle. One of the hardest epistemological tasks is proving a negative, so the debate rages as to exactly what would have occurred had Charles been defeated. Traditionally, the battle is said to have saved Western Europe from Islamic conquest. Edward Gibbon wrote in The Decline and Fall of the Roman Empire that:

[a] victorious line of march had been prolonged above a thousand miles from the rock of Gibraltar to the bank of the Loire; the repetition of an equal space would have carried the Saracens to the confines of Poland and the Highlands of Scotland; the Rhine is not more impassable than the Nile or the Euphrates, and the Arabian fleet might have sailed without a naval combat into the mouth of the Thames. Perhaps the interpretation of the Koran would now be taught in the schools of Oxford, and her pupils might demonstrate to a circumcised people the sanctity and truth of the revelation of Muhammad.

Similarly, Edward Shepherd Creasy wrote in his Fifteen Decisive Battles of the World that "the great victory won by Charles Martel over the Saracens, A.D. 732, which gave a decisive check to the career of Arab conquest in Western Europe, rescued Christendom from Islam, preserved the relics of ancient and the germs of modern civilization, and re-established the old superiority of the Indo-European over the Semitic family of mankind." While modern historians have been more cautious in their assessments, they still ascribe tremendous weight to the battle in terms of the subsequent development of Western Europe.

Indeed, the venerable Sir Charles Oman wrote his seminal work The Dark Ages, "[f]or the future we hear of Frankish invasions of Spain, not of Saracen invasions of Gaul." While Oman is generally correct, most overlook that, even before Tours, Islamic forces had conquered the area in southwestern France around Narbone, which had been considered part of the Visigothic kingdom. Although Charles would launch a successful offensive in AD 737 against the invaders that evicted them from Narbone, Islamic forces would return, not be finally and fully evicted from the region until almost the close of the 10th century.

Moreover, while Tours is often considered a turning point in history, it may have been more a high water mark than a cause. Soon after their defeat at Tours, the Islamic conquerors of Iberia again fell out among themselves. Internal divisions and conflicts, coupled with the emerging threat posed by the nascent Christian kingdom of Austurias (which would become the Kingdom of Leon), may have had as much to do with their inability or unwillingness to mount further attacks into central France as the humiliating defeat they suffered at Tours.