The Christmas Truce is just one instance of otherwise-foes realising they had more in common with the soldiers/agents on the other side than the commanding forces.

Quoth the Steampunk band, The Men That Will Not Be Blamed For Nothing, "I got more in common with the bugger on me bayonet, than the toff that's telling me to stick it in his guts."

See also The Arrangement between Aziraphale and Crowley in Good Omens.

...not shocked about the Adolf revelation. Seems just his flavour.