[@Nate1008] I take it you're not familiar with the BattleTech universe? Not a problem, you're still welcome. 

The short answer to the first question is no, there are no aliens. 

The second answer is that there are many factions in BattleTech. It's a very political setting. Human colonized space is broken up into kingdoms and empires under the reign of long-standing noble houses that go back centuries. We are going to be playing an unaffiliated mercenary company working for one of these noble houses. We may not remain in that houses employ forever, But for the start of the RP we will. That is going to be House Kurita, of the Draconis Combine. 

I'm also going to go ahead and post a link to Sarna.net in the OP. It's the best wiki for BattleTech. It has nearly every scrap of lore on this setting you could hope for.