Other person i believe is right
The German Empire and Austria-Hungary were Allied within the Central Powers, So I assume it was the German Empire in this case, Which Declared war on Russia and France and was at war with Britain due to the Invasion of Belgium.
So the Answer is the German Empire.
The Blitskrieg was the mobile motorized warfare that allowed Germany to overwhelm Poland quickly in world war II
West Berlin was an island of the West, or the Western Curture, or Western sphrere of influence, surrounded by the Eastern Bloc/Western sphere of influence on all sides. It lied in the middle of East Germany, a socialist country, and did not have any direct land connection to other capitalist countries.