For some people the primary social contact that is broken is long running systemic racism.
For some it's militarization of the police.
For some it's the US seemingly slowly sliding in facism
For some it's the economic Injustice of being told "the economy", i.e. the stock market is doing great while unemployment is at an all time high.
Etc
This strikes me as too simplistic solution. I tried to find papers on how demonstrations become riots, but my google.scholar-fu has failed. Anyone got good review papers on this? (If none exist, there is a goldmine there for social scientists.)
In 1773, King George was upping taxes while not providing adequate representation. Colonists thought this was an abuse of power, so they robbed and looted a huge boat filled with tea, which set off events that led to the American Revolution. Look it up, I'm sure there's a wikipedia article or something, it's pretty famous event in history.
Edit, are you also insinuating that's the only 'rioting' they did and then magically the USA just formed out of nothing?