The carnage of WW I produced the kind of revulsion that should have prevented other wars. Hundreds of thousands were killed over battle lines that moved only yards, gas was used for the first time producing horrific deaths and maiming, and there were mortality rates that wiped out nearly 1/3 of the military age male population in France. After the war, combatants set up the League of Nations, located in Geneva with the mission of providing a forum for talking out disputes rather than shooting them out. The League had a very limited charter on what it could do and was hampered from the beginning by the fact that Senate Republicans refused to go along with Woodrow Wilson’s desire to bring America into the League. Part of this was customary politics- if one party favored abolishing disease the other would oppose it as un American- but part was a refusal to see that once drawn into European conflicts America would never retreat from that responsibility again. Indeed, the period of post WW II European peace-now 75 years- is the longest the major nations in Europe have gone without war since the Tenth Century. And it is the direct result of American military presence and NATO.
The League of Nation never had much power. It solved or helped negotiate a few issues throughout the 1930s but because America had acted like ostriches in 1919 and not joined, the League never had to power to oppose Hitler’s militarism in the early years when most historians feel he could have been easily beaten. But what the League of Nations lacked in political and military might it made up for in philatelic power. Issuing hundreds of stamps during its 27 years in business, the League of Nations stamps are listed as Swiss Officials, though they really are as legitimate a separated catalog listing as the United Nations stamps are today.