Berlin was divided into spheres of influence, with the USSR taking East Berlin. Neither FDR or Churchill intended it to be permanent, but Stalin did.

From what I’ve read, he wanted to establish spheres of influence after the war, and wanted the others to agree to it, to the point on insisting to the detriment of war planning. 

That’s how we ended up with the Iron Curtain; those were countries Stalin wanted the USSR to have control over.

Germany was just one of the countries; it was divided because of Nazism, and it was the 2nd time they kicked off a world war. But, the Red Army let the Polish resistance army die before they helped out, and crushed a Czech demand for democracy in the 1960s.

(And before anyone points out Chile, I know we’ve done some of that too, but millions died to Stalin before the war even began.)