Orwell based his fictional nations on real ones and the governments of real Communistic regimes.
In 1984, the concepts of free enterprise and individual freedom no longer exist. Only three superpowers remain to dominate a world of hatred, isolation, and fear.
Oceania includes England (now called Airstrip One) and America
Eurasia contains Russia (and Big Brother is based on the Stalin-like regime of WWII) and perhaps others.
Eastasia perhaps contains countries such as Germany (there are many Hitler-like references and his controlling the German people through fear and manipulation are alluded to frequently).