Chicago's Near 50-Year Cycle of Race Rioting?

Forty-seven years ago, in 1968, Chicago was the site of a major race riot sparked by the assassination of Martin Luther King.  Along with Washington D.C., it helped lead the way to other rioting across the country. 49 years before that, in 1919, another series of riots occurred throughout the U.S., with Chicago, again, being the worst.

Thus far, the protests in Chicago regarding the shooting death of Laquan McDonald have been fairly peaceful.  But, as we all know, peace can turn to violence in seconds. Also understand, that the City's Black Lives Matter people are not merely protesting the McDonald shooting.  They are protesting what they believe to be a pattern of the Chicago police unjustifiably killing blacks for years.

My concern, is that Chicago race riots tend to be contagious and can quickly spread throughout the nation.  Also, should rioting happen, it would confirm a near 50-year recurrence in that city. Hopefully nothing will happen, but if Mayor Emmanuel doesn't resign, it just might.

References:

1968 Chicago Riots: https://en.wikipedia.org/wiki/1968_Chicago_riots

1919 Chicago Race Riot: https://en.wikipedia.org/wiki/Chicago_race_riot_of_1919

List: 1968 Riots: https://en.wikipedia.org/wiki/1968_riots