The closing of entry to Berlin from the west by Soviet forces June 1948–May 1949. It was an attempt to prevent the other Allies (the US, France, and the UK) unifying the western part of Germany. The British and US forces responded by sending supplies to the city by air for over a year (the Berlin airlift). In May 1949 the blockade was lifted; the airlift continued until Sept. The blockade marked the formal division of the city into Eastern and Western sectors.