To say wars are mostly started out of incompetence is an incredibly simplistic generalisation. Wars have been fought for just about every possible reason under the sun. You have wars like the Mongol invasion of China which were fought for power. You have wars like the Crusades which were fought over ideological differences. There have been countless civil wars fought for all manner of reasons whether it be widespread anger towards the nation's leader like in the English Civil War, slavery and state's rights like in the American Civil war, or ethnic hatred like in the Rwandan Civil War. There are also Opium Wars which were fought over trade rights.

Certainly not every war has been conducted with great military planning. But to expect that is the sign of someone who has a poor grasp on human emotions and doesn't appreciate the many varied and complex reasons that we have gone to war over.