For the long years of the Cold War these were the bad guys and idealogical opposites of NATO, the Soviet Union led communist hoards poised on the their side of the IGB, waiting to roll across Europe and expand their area of influence, bringing down the capitalist powers as it went.
While East Germany would have been across the Fulda Gap like a ferret up a trouser leg, Poland and Czechoslovakia (at the least) were less than keen. Their troops were all for a quick change of sides given half a chance and whole divisions would have surrendered to any NATO squaddie who happened upon them.
As it happened Communism collapsed, the Soviet Union lost control of the satellite nations of the pact, the Cold War ended and they invaded anyway in the form of plummers and au pairs and barmaids. Currently there are probably more citizens of the old Warsaw Pact countries in Western Europe now than if they had made a successful military invasion... and that's a lot.
The Warsaw Pact were:-
- Soviet Union
- Albania, later withdrew over idealogical differences, a bit like France and NATO.
- East Germany, joined in 1956