Batman has always been slapping Robin.

Okay so here I understand the war/why can't we be friends connection, but I fail to see how that relates to the batman slapping robin. Am I missing a reference somewhere?

No this just shows the relations between batman slapping robin.

So what is the point of the war scene? I really don't get it.

The war scene resembles a panzer tank and a sherman tank batman being the panzer and robin being the sherman.

I know nothing of tanks so I still don't understand what that has to do with Batman and Robin. I honestly thought you were making a war/why can't we be friends connection (because why can't we be friends is a song by war) but couldn't see how it fit with Batman and Robin. Oh well, I'll leave you to it then.

Sherman tanks are weaker than Panzers.