Short answers, pulled from the story.
The Warsaw Pact was created on the 14th of May 1955 and signed in Warsaw, Poland. The treaty was signed by the Soviet Union and seven other Eastern Bloc nations to counter West Germany's entry into NATO.
The only direct military engagement of the Warsaw Pact was the invasion of Czechoslovakia in August 1968. This operation, known as Operation Danube, involved all member countries except Romania and Albania.
Romania stood alone among the Warsaw Pact members as a country that maintained a significant degree of independence from Soviet control. The Romanian Communist Party issued a declaration on the 22nd of April 1964 proclaiming sovereign rights to choose forms of socialist construction.
The Seven Days to the River Rhine was a Soviet nuclear war plan designed to invade and capture Western Europe in a matter of days. This strategy was kept secret until the archives were opened in November 2005.
The Warsaw Pact officially ceased to exist on the 25th of February 1991. The defense and foreign ministers of the six remaining member states met in Hungary and issued a joint declaration ending the alliance.