Based on the above quote from historian Lewis Gaddis, it can be determined that he believes that

Stalin held little regard for individual rights

national security supersedes liberty

Stalin acted on behalf of his personal environment

the Warsaw Pact was a union of one

If this is the missing quote:

"World politics was an extension of Soviet politics, which was in turn an extension of Stalin's preferred personal environment: a zero-sum game, in which achieving security for one meant depriving everyone else of it."-Lewis Gaddis, American historian

Lewis Gaddis believes that Stalin held little regard for individual rights

Lewis Gaddis believes this thought because Stalin, himself, believes that he is always right and what he decides on is the best decision regardless of what others think.