What significant event occurred when the Soviet Union blocked transportation in or out of a city?

The Berlin Airlift represents a critical response to the significant event of the Soviet Union blocking all ground access to West Berlin in 1948. This blockade was an effort by the Soviet government to force the Allies out of West Berlin, which was situated deep within the Eastern Bloc. In reaction, the United States and its allies initiated the Berlin Airlift, a massive logistical operation to supply the isolated city with food, fuel, and other essential goods through air transport. Over the course of nearly a year, Allied aircraft executed thousands of flights to ensure that the residents of West Berlin received the necessary supplies, demonstrating the commitment to support the citizens of the city during a tense period of the Cold War.

This event is significant because it was not only a humanitarian effort but also a pivotal moment that showcased the tensions between the Western Allies and the Soviet Union, ultimately solidifying the division of East and West Berlin and fostering further confrontations in the Cold War era. In contrast, the other options represent different historical events that did not involve an outright blockade of a city by the Soviet Union, which is the core focus of this question.