This is a tough question because, as Hawking pointed out, we can't apply our logic to an Alien civilization. They may very well have different circumstances as we do and benevolence may not be part of their culture. He particularly mentioned, I paraphrase, that if they have a "war like" culture, they will wipe us out in an instant.
However, assuming that's not the case, then we can deduce that:
Social: The world will probably be more united as we can trade with them and perhaps learn new technology. It will be very much like a poorer country here learning from a more advanced nation and hence rapidly improve their standard of living.
Religious: well, that depends on how advanced this alien race will be. If they can create live, seed other civilizations and do everything "God" can do, then obviously there will be huge changes here. It's hard to say because no one can prove that there's no God and neither can you prove there is a God. So even if an alien race can do wonders, there will always be those who will believe that there's an even higher existence. Of course there might be those who will worship the aliens as "Gods". And certainly there will be those who believe that they are the "devils" and wants to go to war with them.
Political: If you look at history, conflict result from cultural and religious differences. We fight among ourselves because of those differences. Therefore, if we introduce an external factor, there's a good chance political division will be less severe. Perhaps we can finally unit as just "human" race instead of white, black, hispanic, Asians...etc. However, the opposite is just as likely. There could be these pro-Alien group and those anti-Alien group which cause the human race be even more divided. Ultimately it depends on how advanced the alien civilization is because if they are similar to us, the latter is more likely.