Quote Originally Posted by Brandy Blue View Post
I get the impression that the spear and pike (which after all is just a long spear) did not disappear. They could protect missile troops, as they did in Crusader armies for instance, or could provide a screen for beaten cavalry to rally behind. However, it was rare for medieval spear/pike men to dominate a battle field, which is why the Scottish and Flemish victories stood out and impressed contemporaries and historians alike.
The spear and the pike did not disappear per se, it was just the gradual use of a normal spear (something along the lines of a hoplite spear - hoplon) instead of a very long sarissa pike that would have required consistent training beforehand.

Edit: Obviously the Byzantine empire did not suffer a similar collapse of central authority. However, they often didn't have enough soldiers to meet their enemies on equal terms, and so depended on maneuver to cut off the enemy from supplies and reinforcements. A slow, cumbersome army would not be useful.
After the Komnenoi dynasty, so essentially around 1190, the central Byzantine authority collapsed as well but it was not replaced by small, powerful states. It was replaced by other empires.