The problems in Democraticly run cities are sistemic and cultural. They can not be resolved by police or soldiers. All that would be accomplished by marshal law is transferring the ownership of the unsolvable problems away from the Democrats to the federal government.
I think you are right here.
Back in the 1950'S, my family lived in a neighborhood in Indianapolis where blacks became the majority. We were one of the last white families to leave since my father was running a grocery store there. My mother had had enough when she couldn't put clothes out on a line to dry without having stuff stolen. So, we moved away.
The term employed by the media was "white flight". This was about the time that white neighborhoods became locked down with realtors agreeing not to show houses to people of color.
My father continued to run the store for almost a decade. During that time he developed a rapport with the community. At one point, when his store was being robbed at night, blacks in the community told him who the perps were so that he could deal with it.
What the media didn't tell you, which my father learned from his black friends, was that there was also "black flight" going on; i.e., a lot of the blacks were fleeing the crime and bad behavior. This caused blacks to seek housing where they could find relief from misbehaving neighbors. This put quite a strain on black family life for those who wished to raise healthy families. Eventually, they were boxed in by the realtors who wouldn't help them move into safer neighborhoods.
The system has been hard on blacks for a long time.