Without prologue, the story gets right into it. The explosion rocks our heroes are in the thick of it. I guess if you wanted prologue, there were all those "Road to ..." comics, though some of them seemed a bit contradictory.
This issue does a good job of pulling in the reader by the end. Captain America shows us why he is who he is and if you've never been a fan of his, you'll likely have a newfound respect for the character and his abilities, based on one of the best action/characterization sequences from Marvel or DC in a while.
It should be interesting to see how this plays out and which side is "right." If this current political climate in the real world has done anything good, it's given some writers really interesting stuff to work with; to parallel and explore.