The Volturi weren't satisfied with how we were acting, so they found a place that had five factions and they trapped us there. They created a shield around the fence that would block any vampire that tried to escape and the only person who could take down that shield was Bella. And Bella wasn't vampire yet. This was the Volturi's way to convince Edward to turn Bella vampire. They wanted to take advantage of her power, but what they didn't know was that Bella was a shield and her shield could penetrate through the volturi's shield. If you wanna know what happens while they are trapped in divergent then you should read the next chapter.