In 1968, the Soviet Union along with several Warsaw Pact allies invaded Czechoslovakia with the intention of re-establishing a full communist government. The reason for the invasion was mainly due to "Prague Spring" - the period of great hope for the Czech people led by the reform movement against the hard-line policies of the Czech and Soviet governments. The main justification given by Soviet Premier Brezhnev regarding the attack was that the USSR, a communist nation itself, had an obligation to stop anything that poses a threat to established communism in any country. This came to be known as the "Brezhnev Doctrine", and was seen as a clear warning to other eastern European countries. This example is one of many in history that has raised the issue of whether or not great nations are justified in exerting influence over the affairs of lesser states.

The issue of whether or...