Need some arguments for debating teacher

[Luca]

Idk if this is the right place to ask this question. But I am in the following situation:

I am in history class and we discuss the creation of the BRD(West germany) and I asked why the allies split germany between austria and germany, instead of unifying it.
The only answers I really got were that it is racist, and these people are not german but austrian (because of "different culture"). It would be the same as asking "Why aren't America and England a unified country".

I see this as a stupid argument of course, but still I couldn't find many good arguments to counter them.

And because I know all of you are really into politics, so maybe you could help me out a bit and give me some advice?

[Odin]