forum.freeciv.org

It says "can prevent declaration of war in some instances", but also "if any player's city is in revolt for two turns, that player's government falls". But isn't this automatic for Democracy and Republic? Dos this mean that, when UN is in effect, Monarchies and others can also fall?

(Also, where can I find out when a wonder gets obsolete?)

In the multiplayer ruleset, Republic and Democracy automatically have a senate preventing declarations of war without a reason, and Democracy fails if a city is in civil disorder for two turns. With the UN, both of these are the case regardless of your type of government. So yes, even a Despotism can fail if the people are revolting.

Additional trivia: The UN effects don't survive the destruction of the UN (which is a bit weird), so by destroying the city where it is built, in can be disabled.