Follow up question: say humans learn about wizards and maybe even have some anti-Voldemort wizards on their side when he tries to take over. What stops IEDs, sniper teams, hypersonic missiles, or even just random citizens with a gun or a knife from being able to kill unsuspecting death eaters whenever they venture out from secure fortresses?
Wizards seem pretty effective at stopping threats they can see, but if say Malfoy was going through London cursing people and blowing stuff up, what stops a pissed off dude with a rifle from shooting him from a 3rd story window? In Iraq they learned helos used telephone poles to navigate so they strapped IEDs facing upward on the poles, you could take out a lot of broomsticks like that.
Not saying it wouldn’t be a costly war and we would lose hundreds or even thousands for every wizard, but I don’t think it would be a cakewalk like everyone else seems to be saying.