The Soviet blockade of West Berlin

This is a tough one, but most likely to prevent the creation of west Germany. Let me explain:

The original Berlin blockade was a sort of “punishment” after the western allies introduced the German Mark, a new currency introduced in western Germany to help stabilize Germany. The goal in this was not only to “punish” the western allied powers, but also to force them into handing western Berlin over to soviet occupation forces.

So essentially, the answer is most likely to prevent west Germany from forming.

Hope this helps!