The Walking Dead Season 6 Finale: 10 Things To Expect When Negan Arrives

Alexandria may have walls, and weapons, but it's far from being a completely safe-zone, and that's only going to intensify once Negan shows up. 

After killing Glenn, he makes a similar demand to that he already has of Hilltop Colony: half of everything they own, otherwise more people will be killed. 

He'll come by personally in order to make the collection, and have various run-ins with the people of Alexandria, most notably Spencer Monroe, who questions his identity the first time, and the next he actually kills him, all while taking whatever he wants while no one can stop him. For example, he takes medical supplies (Denise is still alive at this point, unlike the show), and states that the wall is the only medicine Alexandria needs. 

Also, killing Spencer reveals just the kind of humour we should expect, as he delivers the killer line: "Oh, how embarrassing! There they are! They were inside you the whole time. You did have guts. I've never been so wrong before in my life!"