The great migration occurred in the early 20th century. It caused racial tension because there was a struggle for living space in the frequently congested cities. While discrimination was not sanctioned in the North (as it was in the South), intolerance and racism were extensive.
Increasing rents in isolated areas, plus a resurgence of KKK movement after 1915, worsened black and white relationships over the land. The summer of 1919 created the largest time of interracial conflict in U.S. history, including a severe twist of race protests. The most severe took place in Chicago in July 1919; it remained 13 days and transmitted 38 people lifeless, 537 wounded and 1,000 black households without shelters.