The UN was specifically designed to fix all the problems that caused WW2—including the dinked design of the LoN, which failures were specifically addressed by dissolving it in favor of the UN.

How come the un succeeded to stop ww3 whereas the league of nations failed to stop WW2?

So, if it’s word-for-word, then yes, that’s bogus, and has the refutation I summarized.

I’ve elsewhere also debunked the myth that the middle ages (not the same thing as the dark ages: conflating them is also a fallacy I have called out many times) invented everything (or even a significant amount of anything).

So, you are, alas, reading rank apologetics and not any honest, logical, or accurate assessment of world history.

As for your question:

The UN has prevented any other global war since. That was, in fact, the purpose of it: to establish international diplomatic relations and processes to quell the causes noted in hindsight of previous world wars. The UN also created the international framework based on human rights being more important than selfish national desires for territory or wealth, and thus a goal and controlling limit to put on any negotiating table. That didn’t exist before WW2. And it has changed the entire way global aggression is framed and discussed and policed.

The argument is repeated word by word here along with all sorts of other questionable claims like the church not being really to blame or the middle ages having technological innovations:
https://www.brianpavlac.org/witchhunts/werrors.html#cruelty

What did the UN actually do that made the world successfully avoid ww3 and ww4?

I’m not sure who makes that argument or if that is the argument they actually attempted, but there are a number of hopeless confusions here.

First, Better Angels and Moral Arc already ran the numbers and found that you are describing availability bias: conflating large events with productive events; in fact, more people were killed in previous centuries, per capita, while the era of mechanized world wars actually reduced the death rate (e.g. WW2 produced the UN and thus now nearly a hundred years of relative global peace despite a massive increase in global population; and produced less deaths than most large war eras by moving faster to its conclusion). Likewise all other moral metrics (crime, slavery, gender inequity, income inequity, access to human rights and medical and educational systems, etc.).

Second, “the Dark Ages” are called that (and criticized as “barbaric”) not for its death rate (though that was enormous: the population loss caused by civilization collapse was catastrophic and has never been equalled since) but for the massive loss of knowledge and massive decline in civilization (collapsing economies, particularly trade, industry, and agriculture, as well as science and technology), leaving centuries of relative ignorance and low sophistication of civilization. The term was coined to contrast it with the Renaissance, called a “Rebirth” specifically because of a recovery (hence “rebirth”) of all the things lost: knowledge, economies, scale of industry and agriculture, scale of popularion, and sophistication of the engines of civilization, like education and government, and science and technology.

Reddit is a garbage pit of ragelords and asshats with hardly any relevant knowledge or competence worth heeding.

Please choose a more reliable source to get your information from.

Hey man, why in reddit, bad history group, claim the dark ages didn’t really exist.

I haven’t evaluated the claim of “closing trade routes,” though at a glance that sounds implausible to me.

The Byzantine Empire (the “eastern” Roman Empire) maintained sufficient wealth to avoid the catastrophic collapse of the West. It declined more slowly. Islamic expansionism had something to do with that, but as much to blame is the Christian mindset that dominated it, which still ended all substantial scientific and technological progress even in the east, and continued making bad economic and political decisions: I find the Wikipedia summary to be a decent starting point, along with a decent summary of the economics at The Collector.

Does this mean the eastern Roman empire completely avoided the dark ages?

Some people try to argue that the expansion of Islam exacerbated the dark ages by closing trade routes or sth, how plausible is this claim?