Most of Europe didn’t have any significant amount of slavery to ban. Even then, there was considerable resistance - France abolished slavery during the French Revolution (a time of civil war, if you will remember), then reimplemented it, then abolished it again. Most of Latin America abolished slavery only with wars of independence; many of them not even then, having civil wars of their own during which the issue was resolved. Brazil had a coup over abolishing slavery, much of Africa and the Middle East retained the institution until stripped of independence (via war) during the colonial era… the list goes on.

Wars over slavery are presented any time there is a powerful slave-holding elite in a post-Enlightenment society.