[Deuce]

I'm already certain of what happened to turn my once sweet but slightly apprehensive dog into a little evil creature that children run away screaming from at just the sight of his fuzzy face. What happened wad we moved from a cute little house in Italy to a mostly quiet apartment in d.c.
I'm not sure what to do though, we've just moved into an apartment complex and Rizzo won't behave on his leash anymore. I have to keep him right on my heel to keep him from running at dogs 100x his size, and every time he spots a stranger he starts to growl and tries to run away. In other words a walk is now chaos and massively embarassing, and he seems to be on constant edge in the house. We've only been in here for a couple days but I don't want this to be a habit formed...any tips on curbing this behavior before I cant take him out of the house anymore without me having to wear a paper bag over my face?