If america was invaded would street gangs....?

Yeah I personally think they could pose a threat, depending on what weapons they have and how many are part of the gang. And of course, how much experience they have in combat. If say, 10,000 members of a gang were unexperienced and faced a 5,000 men trained army, they still have a decent chance of losing. Anything is possible, and that's how revolutions start. It's pretty much happened already. When America rose up against Britain during the Revolutionary War (1775-1783) the majority of the soldiers (even the ones led by Washington) were unexperienced rag tag soldiers who could be viewed as a "gang" in some sort. They were a group of people who came together for a certain cause and trained until they could fight their way to victory, against one of the most powerful nations at that time. They succeeded. Anything is possible. And this situation would be awesome to imagine.

Not really.

Heavily armed doesn't equate to training and expertise. An invading army would have that, as well as body armor, heavy explosives, better communications. Also more ammo, far better maintained guns, would work better in small teams, know how to set up ambushes, lie in wait, etc, etc.

Gang members just pretend to be like soldiers, but soldiers don't have to pretend.

Yeah, absolutely.

Yes, serious increase in crime.