Stalin cut off supply lines to democratic West Berlin.
Explanation:
All of Berlin was in Soviet Union occupation zone as declared at end of WWII.
However West Berlin was split between USSR having East Berlin and British/American and French having half of the capital like half of Germany itself was split up.
Stalin cut off all land transportation routes into the Allied zone. Fortunately Allied/American air transport kept West Berlin supplied with necessities of food, fuel, medicine etc. Until Stalin had to give up his Cold War attempt to capture all of Berlin without armed conflict.
