Which factor created a risk of a war between the allies and the soviet union?
a)the soviet annexation of eastern romania
b)the signing of the warsaw pact in 1955
c)the soviet blockade of west berlin in 1948
d)the soviet takeover of the baltic republics

The correct answer is C.

The Berlin blockade was performed by the URSS in 1948 and lasted for approximately one year.

The city of Berlin had been divided in four sectors, exactly in the same manner that the whole German territory was divided and splitted among the victorious Allied countries after WWII. US, UK and France unified their territories and created the Federal Republic while URSS created the German Democratic Republic on the Eastern the side, which remained independent from the other three . The city of Berlin was divided in four as well, but the city was actually embodied within the Eastern region of Germany under the control of the Soviet Union.

This is why the URSS could block supplies and impede ground communications with West Berlin, the area of the city controlled by US, UK and France. The so-called Berlin airlift was organized to acess this area of the city by plane, in order to bring supplies.