How did the crossbow change medieval warfare?

The crossbow doesn't show up until the late Medieval period and was the first handheld weapon that could be used by an untrained soldier to injure or kill a knight in plate armour. The most powerful could penetrate armor and kill at 200 yards. They were easier to arm than longbows because the crossbowman doesn't have to use a hand to hold the string back while aiming and it can also be loaded faster than a longbow. They require less upper body strength to operate and can be used with both arm to span the crossbow. The Medieval bow was very inefficient and were used for war or sport. The larger ones were used to defend fortifications while the smaller ones were effective in open battle when used correctly. They were very expensive and only the wealthy could afford them. Assassins liked to use them and there were a number of laws that address this problem in particular.