Racism, Because lately with all the riots and marches, were caused by it, the effects were the most expensive riots in U.S history and just alot of violence.
A lot of people find racism to be the greatest social problem around the world because it can happen to anyone and anywhere. It's led a plethora of conflicts and even some wars. The effects on society can be division, prejudice, etc. We've seen in the United States and in other places what racism can do. Take the early 1900's for example. African Americans were viewed as inferior to white people because of their skin. This is a clear definition of what racism can do to people.
