Essay:American law enforcement war on African Americans in the twenty-first century
The United States is a dangerous place for members of certain minority groups. This has been true since Europeans first "discovered" America and began slaughtering its inhabitants. Apparently genocide of native North Americans wasn't enough to sate European bloodlust. Through a combination of economic immorality and religious zealotry, Europeans began kidnapping Africans, packing them into death ships, and enslaving the survivors.
After a number of centuries, some of the European Americans finally found slavery to be problematic enough to fight one of the deadliest wars to date. This resulted in "emancipation", at least in law. The follow through wasn't so great, and Europeans (now Americans) found ways to use their legal system to continue systematic oppression and murder of African Americans that fell just short of genocide.
And that was only the first few hundred years.
In modern America, state violence is still responsible for a great deal of African American death and incarceration.
Racial violence in North America began with the arrival of Europeans. The new settlers immediately began to fight the populations of North Americans in order to subjugate the land. As they slaughtered, enslaved, and drove out the first Americans, fertile land became available for farming, and rather than applying hard work, the colonists kidnapped Africans to work the land for them. Although European settlers were for a long time outnumbered by Native Americans and African slaves, they were able to maintain their dominance by violence, but at the individual and state levels.
Violence Against African Americans Pre-21st Century
The kidnapping and enslavement of Africans began as soon as Europeans began to colonize the Americas. The brutal African slave trade was notable for its high mortality, estimated at about 12.5% during the voyage itself, but as high as 50% if capture, transport, and acclimation to America are included. 
African American slaves were legally emancipated during the Civil War, but until the South's defeat, this was in law only. During the post-war period (known as Reconstruction) white southerners, furious at the loss of the legal right to own other humans, passed laws limiting the rights of blacks, formed formal and informal organizations to oppress former slaves, and murder of blacks was frequent and largely unpunished.
The legal system for the oppression of African Americans that developed after the war is known as "Jim Crow". This legal framework was upheld by the U.S. Supreme Court in the infamous Plessy vs. Ferguson decision which declared that "separate but equal" was just awesome. It took nearly 50 years for the Supreme Court to reverse this precedence in Brown vs Board of Education. By that time, however, the formal structure of laws and violence were entrenched.
20th Century Race Riots
The 20th century saw many acts of mass violence against black Americans. Some of the most infamous were:
- East St Louis 1917: at least 100 African Americans murdered by white mobs 
- Chicago 1919: a black teen swam into a segregated swimming area and was murdered by whites. Days of rioting left hundreds homeless, more than a dozen whites dead, two dozen black Chicagoans killed, and over a thousand black families left homeless when their homes were burned.
- Tulsa 1921
Police Violence in the 21st Century
...specific examples, mass incarceration, systematic suppression of dissent (https://www.theroot.com/did-nypd-spy-on-black-lives-matter-protesters-judge-ru-1831805889)......