The correct option is C The Principle of Collective Security
The basic idea behind the formation of the League of Nations was that aggressive war was a crime against all of humanity, not just the nations directly involved in the conflict. This is why the Principle of Collective Security was adopted as one of the key founding principles of the League. According to this principle, an aggressor against any one state is considered an aggressor against all other states, which act together to repel the aggressor.