Primarily, the Berlin Blockade was an episode in the Cold War – Stalin was taking over eastern Europe by salami tactics, and America had just adopted the Truman Doctrine.
Secondly, America and Russia had different Aims for Germany. Stalin wanted to destroy Germany, and was stripping East Germany of its wealth. Britain and America wanted to rebuild Germany’s industry – in January 1947, they joined their two zones together into Bizonia.
On 31 March 1948, Congress voted for Marshall Aid. Stalin (rightly) saw this as an attempt to undermine Russian influence in eastern Europe. The Russians started stopping and searching all road and rail traffic into Berlin.
Finally, on 23 June Britain and America introduced a new currency into Bizonia. The next day the Russians stopped all road and rail traffic into Berlin. The Americans thought Stalin was trying to force them out of Berlin. Stalin claimed the new currency was an attempt to wreck the East German economy.