For want of a horseshoe…

What we do know with absolute certainty is that following the Muslim conquest of Egypt, the rest of North Africa, and Spain, the wheel disappeared from this whole area. For centuries there were no carts or wagons. All goods were hand-carried or packed on camels, donkeys, or horses. This did not happen because the Arabs lacked knowledge of the wheel, but because they thought it of little use. In their judgment, wheels required streets and roads. Camels and pedestrians required neither. Moreover, given their disdain for the wheel, it is doubtful that Muslims knew how to construct a proper harness to hook draft animals to carts and wagons.
In contrast, sometime early in the “Dark Ages,” Europeans were the first to develop a collar and harness that would allow horses rather than oxen to pull heavy wagons—with a very substantial gain in speed. … The pulling capacity of European horses was increased again when, in the eighth century, iron horseshoes were invented and came into widespread use by the next century. …

Any objection that Arabs may have had to wagons is that those in use at the time of the Muslim conquests and before had a fixed front axle that made them difficult to turn. They also had no brakes and could be very dangerous on downward slopes. By no later than the ninth century Europeans had solved these problems.

-Rodney Stark, God’s Battalions: The Case For The Crusades, 67-68