Complex sentence: The only alternative was to replace knighthood as the core of military forces with mercenaries, as under a condottiere, but those often proved highly unreliable and expensive, as well as being known for changing sides for greater profit, or simply deserting and looting for themselves.
Split into simpler sentences: The only alternative was to replace knighthood as the core of military forces with mercenaries, as under a condottiere, but those often proved highly unreliable and expensive. As well as being known for changing sides for greater profit, or simply deserting and looting for themselves.