The killing of unarmed blacks like mike brown started it ?
In the United States immigrant communities became a larger political influence in the early 19th century because of their dramatically increasing numbers. There were a large number of Irish and German immigrants coming to the US at this time due to famine in Ireland and political persecution in Germany. In response to the large influx of immigrants and their potential to influence the political system different groups of Americans took on anti-immigrant or "nativist" views, being strongly against the influx of immigrants and feared that these new immigrants would take their jobs. In response the Know-Nothing Party was formed to opposed this increased immigration politically.
Truman defended the Truman Doctrine that meant that if a capitalist country was being attacked America had a duty to give military aid to that country. Truman also knew that the invasion of Korea by the USSR could cause a domino effect and they would dominate one country after another. He had this knowledge since WWII with Germany’s actions.
Actually Columbus was an evil man he didn't care the natives who was there before he got there and he stole from them.