What was the חטא of the דור הפלגה?
The Ran in his Derashos (Drasha א) has an interesting explanation. He explains that really they did no sin and that there was no punishment. He says that they wanted to have 1 world government. This is not an aveira but it is something that Hashem does not want. 1 world government means that there is nowhere to run. If Nimrod had ruled the world Avraham would have had nowhere to go. Therefore Hashem split them up and created nations and languages so that there would always be somewhere for the believers in Hashem to run to. The Ran writes that this has applied throughout history to the Jewish people up to and including his time. We know that from the Ran's time until today the same thing has applied. Whenever we were kicked out of 1 country a different country took us in.
Based on this, we should be concerned about the UN and the push to 1 world government. As the Ran says this is not Hashem wants and is bad for the Jews.