Maximum Holding Strength
For a trailer purporting to be about Strongholds, it tells us very little about them. Though we do get some dialogue about joining one providing Max with the solace he desires. Which sounds rather counter-intuitive, I'll grant you, but does also make a degree of sense. After all, it's much easier to be left alone when you're surrounded by people who know you want to be left alone, and don't want to murder you in the face to steal your guzzoline. Or spleen.
What little we do see of the actual stronghold stuff suggests that, uhm, I don't know actually. Perhaps you'll be able to build fortifications? We're told that there are several different factions, all with their own base of operations and that there will be chances to form alliances with some of them. But the ultimate goal is a nebeulous find "the pieces essential to [Max] puzzle he tries to solve." There's going to be some "deep" car customisation though. And lots of punching people in the face until they die.
Mad Max is currently set to be released on September 1st, 2015 across all major platforms.