I expect that for many I am preaching to the converted, but here goes:
You have created a vicious circle for yourselves.
Your populace is armed to the teeth, awash in guns, with no other country in the world having anywhere near the same rate of gun ownership. Estimated number of civilian guns per capita by country - Wikipedia
Gun ownership is entrenched in your constitution, and proponents such as the NRA are so rabid in their beliefs that they have a religious fervour.
So many of your people have been shit on and shot at for so long that your police rightly fear being shot on the job.
That has created a paranoid police culture broadly supported by the judicial system and a significant portion of the middle and upper class, which in your country is predominantly white.
The paranoid police culture protects itself by routinely shooting first and asking questions later, and obfuscating and/or covering up if needs be.
This has created further conflict with the lowest class, which in your country is predominantly black or brown.
Your nation was founded on slavery, with roughly half of it fighting bitterly to keep it despite other European powers having such as England having given it up decades previously.
Where slavery left off, Jim Crow picked up, with lynchings, beatings, burning of churches, segregationist laws, gerrymandering, race based disproportionate funding for health and education.
Where Jim Crow left off, your GOP picked up, from the top right down to local school boards, with race based gerrymandering and race based disproportionate funding, particularly concerning education.
When comparing NATO country incarceration rates, you are literally off the chart, bearing no comparison with the other countries. https://static.prisonpolicy.org/global/incarceration-rates-nato.png
You have the second highest incarceration rate in the world, second only to the Seychelles, a country of 92 thousand people, not including the Somalian pirates jailed there. List of countries by incarceration rate - Wikipedia
Blacks are grossly over-represented in your prison system, and your prison system is brutal.
That leaves you facing several inextricably intertwined massive problems.
Entrenched racism, with economic and political power held by whites, and blacks being warehoused in the prison system.
High barriers to moving up in economic class, hitting blacks the hardest.
Entrenched gun fanaticism by whites held as fervently as a fundamentalist holds religious belief, and a country that is awash in guns.
If you ever want to join the first world when it comes to having good relationships between the police and the populace, you are going to have to change. Rather than try to do this, you elected Trump. You’re not even a full democracy any more. http://felipesahagun.es/wp-content/uploads/2017/01/Democracy-Index-2016.pdf
Want to pick up your socks?
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Organize to get out the vote and to make your votes count, and push your politicians constantly.
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Confront racism at every opportunity.
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Confront your gun cult at every opportunity.
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Don’t sit on your fat ass and whinge, and stop deluding yourselves that you are the land of the free, for you are not. Not even close for millions of your citizens.
If you work very hard at it, you might be able to turn yourselves around in a couple of generations, and it will be well worth the effort.
If you do not, the rest of the first world will continue to pass you by.