There have been proposals for an independent force under the control of the UN.

How independent could it really be? Who would be giving the orders?

The UN General Assembly? That has all the disadvantages of a non-representative democracy - tyranny of the majority and so on. Plus the disadvantages of deciding questions of law and morals by vote. You'd get big alliances or parties sticking together right or wrong, and demanding rent from others (join us in votes or we'll vote war on you).

For instance what if all the Arab countries voted for war against Israel? What a bunch of countries voted for war against some little county you never heard of? I don't want to rely on the other countries diligently fact-checking every time when they suffer no repercussions for making mistakes.

What if votes were by UN GA with veto power to a few big countries, like today's GA resolutions? That just means those big countries, like the US, are above the law and can also grant their proxies and satellites above-the-law status. And because these countries aren't afraid of ever being voted against, they don't care much (from symmetrical considerations) about enforcing the law correctly against other countries. Instead they enforce the law only in their own interests.

Plus, in any war declared by a voting body like the UN, the voters are liable to cancel the war after the first battle gone wrong.

OK, what if decisions were made by some International Court of Justice? Well, how would you elect the judges to this court? Or do you want 1000-judge panels with a judge from every country? That would be the same as voting.

For various reasons the kind of nations that are going to be involved in enforcement are going to be more democratic, more liberal, more legitimate and more powerful than the states run by war criminals.

Why is that? I think a much simpler explanation for the state of affairs today, and a much better predictor of the future, is - the nations involved in enforcement are going to be whichever nations belong to the most powerful military and economic global alliances. They have to be to be able to enforce judgments against anyone else; and they do it to protect their own economic interests.