A world government with a force would be an interesting concept. Corrupt African states has lead to their citizens fleeing to Europe with EU solutions being band-aids like giving Libyan coast guard ships and money to prevent the ships from leaving Libyan waters, the better solution would be to fix corruption and help development in the refugees' home countries, but the EU governments can't do that, can they (giving the governments money would just mean the leaders would be able to afford a new villa and a few more Mercedes Benzes).
They could directly invest in infrastructure (coupled with suitably sized bribes, which can be kept to a small portion when done directly), which is what China is doing.
But they'd get accused of colonialism if they actually tried to help directly like that (and perhaps it would be true). So they're left in the untenable position of dealing with mass migration or funding warlords.
Not all of them make it. The vessels aren't particularly seaworthy, and they're not allowed to dock, so effectively they dump their passengers in open boats and rely on the coastguard rescuing them and taking them to Italian soil.
TL;DR: Regime in cambodia genocides about 1/4 of its population between 1975-79, is removed from power by Vietnam. UN helps recovery from destruction of society by previous govt & transition to new govt which after some initial chaos stabilizes. It's still not a proper democracy, but at least it isn't genocidal.
Considering the extremely difficult circumstances (a genocide so bad that it destabilized society & vietnam being an authoritarian regime), I am actually impressed by what the UN managed to pull off.