what led to the Berlin Blockade?

Answer 1

Stalin's USSR (Russia) was not happy about the Allies (especially America) working to build up the West German economy in 1947. The Russians viewed a resurgent Germany as a threat to them. This was understandable considering Russian losses at Germany's hands in WWI and WWII.
The Berlin Blockade was a way of expressing Russian displeasure and getting back at the Allies/Americans.
The USSR had to be careful though. They did not yet have the atomic bomb (but would shortly after the blockade ended). The Berlin airlift was our (American) response to the blockade. This was one of the early scuffles of the Cold War.

Answer 2

If you're speaking of the Berlin Airlift, the blockade was set up by the Soviets to prevent the Americans from interfering with their handling of the situation in East Berlin/Germany (militarily, economically, etc.,) and therefore prevented aid from reaching the East by road with the blockade.

If you're not speaking of the Berlin Airlift, please specify what you ARE speaking of.