An interesting thought, however, a UN-like organization pre-ww1 is very unlikely. It would require member states to respect each other's territorial integrity. That goes against the imperialist interests of Britain, France and Russia in particular. But suppose such an organization is set up at the
1899 Hague Peace Conference.... What could it achieve?
What could it do, for example, with regard to....
- South Africa, where Britain wanted to annex the independent republics during the Second Boer War, committing war crimes against the civilian population (including concentration camps).
- The growing Russian influence in northern China with the Russo-Japanese War as a result.
- Morocco, which the French claim as a protectorate.
- The Ottoman Empire, against which Italy begins an unprovoked war (with the approval of Britain and France).
- The Balkans, where the Balkan states also begin a war against the Ottoman Empire (with Russia's approval).
All in all, I think such a UN-like organization will indeed be a paper tiger....
However, I think that such an organization could have played a role during the July crisis of 1914 and thus possibly prevented WW1. If this organization had the authority to send a mission to Serbia to oversee the investigation of the terrorist network that committed the killings in Sarajevo, there would have been no need for Austria-Hungary to issue an ultimatum. But it is likely that Russia will veto such a mission. Russia (and France) preferred war rather than recognize that Austria-Hungary was entitled to justice.