It occurred to me recently that, although there have been limitations on the production and/or deployment of various types of weapons - MRBMs, biological and chemical weapons - there never seems to have been any serious attempt at a reduction in weaponry and armies overall. Yes, the Versailles treaty could be taken as an example, but it was one-sided, and too easy to circumvent or outright break.
What would it take for this to be seriously attempted at some point in the 20th century? And preferably, (generally) successfully implemented.