The League of Nations
The League, with headquarters in Geneva, is the main forum for resolving disputes between its member states. With the exception of China all of the main power blocs send representatives to the League and for the most part obey its directives and decisions. It’s generally assumed that if any of Earth’s colonies become independent they will also join the League.
As originally constituted the League was virtually toothless, and would have been unable to do anything really effective to defend the peace, but in 1935 Italy invaded Ethiopia, and Britain (perceiving the invasion as a threat to its African colonies) blockaded Italian Somaliland, claiming to be acting in defence of League principles. While this was barely justifiable, it set a precedent which led to the defeat of the German occupation of the Rhineland in 1936; Britain blockaded Germany while France sent a division into the Rhineland and drove out the Germans. Recognizing that this was likely to set the pattern for future wars, the League treaties were amended to legitimize future interventions.
Eventual results included the slow declines of Fascist and Communist dictatorships in the forties and fifties, with every move to expand their territories blocked before it could really begin. Gradually the League expanded its membership and mandate, opposing militarism and promoting civil liberties, and was one of the principal factors in forming the world as we know it today.
The League controls Earth’s space fleet, which currently consists of eight ships provided by various countries. It is used mainly for piracy suppression and rescue operations in the vicinity of the Earth, but patrols occasionally take in Venus, Mars, and the outer worlds.