Based on the DC Comics series from Riccardo Burchielli and Brian Wood of the same name, the demilitarized zone of Roberto Patino’s four-part HBO series “DMZ” can be full of surprises. It’s what we know as Manhattan, after a civil war between the Free States of America and the United States of America. We initially see the DMZ as a place of ruins, of sprawling weeds taking over once busy intersections, but then realize the possibility it shows. There are no police; the McDonald’s sign is a mere trash heap; different neighborhoods have created their own vibrant communities, like the gangs in Walter Hill’s “The Warriors.” It only looks like “I Am Legend,” especially when we get a sense of the 300,000 people making it their proud home. “DMZ” can be compelling however emotionally broad in observing what parts of our modern humanity would survive in a potential war zone, especially when a new democracy is at stake.