Why???? because the gangs may be his new national army stronger and just as well equiped as the military. If you arm every prisoner in the country and give him or her a free ticket to freedom if thye would pick up and fight you bet they will have an army
No! What you would have is a mob, at best.
An army is disciplined, and works together as a unit.
These thugs would mostly be at each other's throats as much as anything else.
At the first opposition to their "army", the "battle" would resemble what happened to the Midianites when Gideon and his 300 attacked their camp. (Judges 7)
Pish-tosh. A bunch of crooks with guns is Chicago, where they kill each other. An army has direction and discipline. Have you ever seen "Zulu"?