Tomorrow Belongs to Me - Cabaret
The patriotic song from Cabaret, in the beergarten in pre-war Nazi Germany, sung by the arian Hitler youth. You see many young and old people getting taken up by the song, but you can also see the old man who remembers WWI and knows what will happen.
https://www.youtube.com/watch?v=_tUctFu46_c
Powerful. Yes, that old man knew.