Black Day In July

I was just wondering if this song was about an actual event. If so what was it ? I have been listening to the lyrics and trying to figure it out. If anyone knows could they give me a hint

[closetcanadian]

This song chronicles riots that took place in Detroit in July 1967. For full details go to:
http://www.walkervilletimes.com/26/black-day-july.html

closetcanadian

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"be calm in the face of all common disgraces...and know what they're doin' it for..."