Nazizm - you are right.
But soviets? why? they genocided christians,not jews,and jews were still part of ruling establishment there.
They could always say,that they always supported Jahwe.
Lie,but so what ? entire system was made on lies , lasted till 1991,and fall becouse of economy,not Jahwe.
Christians - protestants are,like Heine once said,jews who eat pigs,so they would convert,maybe muslim,too.
But normal Christian - why ? catholics never relied on God fighting battles,popes prayed when muslim invaded,but fought them with coalitions of countries created by them.
And we have enough genuine miracles,like Fatima.
Reaction of normal catholic would be "it is not work of God",and we would remain the same.