What else would it be? I don’t see how one could blame WW1 on a single person. Though I would say most of WW2 could be blamed on a single person, if you really feel like it.
No need to refute Marx, reality has already proven time and time again that communism doesn’t work in practice.
Btw your argument only applies to “pure” capitalism, without any government interference. Homelessness is not really an issue in many European countries.
I think it would be quite reductive to just blame the assassin. Sure, he was the one that created the spark that ignited the conflict, but it had been brewing for years, and we can’t ignore the roles the heads of states were playing in starting the war.