The city of Detroit's crime levels have declined since the 1970s, but in 2007 it still had the sixth highest number of violent crimes among the twenty-five largest cities. The city has some of the highest levels of poverty in the United States. The influx of immigrants to Detroit during the first half of the 20th century along with economic and transport improvements following World War II led the wealthy, primarily white population to move to new suburbs in what was known as 'white flight'. Non-whites were actively prevented from moving to the suburbs in many states through legally sanctioned exclusionary covenants preventing them from obtaining mortgages or even purchasing property at all. In Detroit, the 12th Street Riot in 1967 contributed to this effect. A police raid on an unlicensed bar frequented by African-Americans stirred already existing social tensions and led to violent confrontations between the police and civilians, with 43 people killed, hundreds injured and several thousand buildings destroyed. Today the population of Detroit is over 80% black, while its suburbs are mostly white. To counteract racial tensions, Grosse Pointe Interfaith Center for Racial Justice was set up in 1967 and in March 1968, weeks before his assassination, Dr. Martin Luther King, Jr. gave a speech at Grosse Pointe High School sponsored by the Human Rights Council.