Sundown towns
"Beginning in about 1890 and continuing until 1968, white Americans established thousands of towns across the United States for whites only. Many towns drove out their black populations, then posted sundown signs... Other towns passed ordinances barring African Americans after dark or prohibiting them from owning or renting property; still others established such policies by informal means, harassing and even killing those who violated the rule... Outside the traditional South—states historically dominated by slavery, where sundown towns are rare—probably a majority of all incorporated places kept out African Americans."
— James W. Loewen, Sundown Towns
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A sundown town is a town that is whites only, particularly after dark.
Although Americans typically associate racism with the Deep South, sundown towns are primarily a Northern and Western phenomenon. Because of the South’s historical dependence on black labor, Southern communities needed black residents—they oppressed and exploited them, but tolerated their presence. Elsewhere in the country, however, blacks and other people of color were regarded as "undesirables", and during the late 19th and early 20th centuries, hundreds of communities forcibly expelled them, while newly formed towns and suburbs were often designed as whites only from the start.
Once established, sundown towns maintained their whites-only status though the use of warning signs, aggressive policing, racist laws and housing covenants, and vigilante violence. An article in the December 7, 1905 edition of the Fairmont, West Virginia Free Press describes how children in Syracuse, Ohio served as the town’s first line of defense against black people:
In Syracuse, Ohio, on the Ohio river, a town of about 2,000 inhabitants, no Negro is permitted to live, not even to stay overnight under any consideration. This is an absolute rule in this year 1905, and has existed for several generations. The enforcement of this unwritten law is in the hands of the boys from 8 to 20 years of age...
When a Negro is seen in town during the day he is generally told of these traditions... and is warned to leave before sundown. If he fails to take heed, he is surrounded at about the time darkness begins, and is addressed by the leader of the gang in about this language: "No nigger is allowed to stay in this town over night. Get out of here now, and get out of here quick..."
If he hesitates, little stones begin to reach him from unseen quarters and soon persuade him to begin his hegira... So long as he keeps up a good gait, the crowd, which follows just at his heels, and which keeps growing until it sometimes numbers 75 to 100 boys, is good-natured and contents itself with yelling, laughing, and hurling gibes at its victim. But let him stop his "trot" for one moment, from any cause whatever, and the stones immediately take effect as their chief persuader.
When traveling by bus or train, African Americans had to take care not to get off at the wrong town. Staying aboard wasn’t always enough; black porters on trains passing through areas where anti-black sentiment was high would sometimes hide during station stops. Black automobile drivers, of course, were also at risk, especially if they got lost or broke down in the wrong place.
In the latter half of the 20th century, as public attitudes towards racism shifted, many white communities suppressed or forgot their own histories. People grew up in sundown towns without being consciously aware that they were sundown towns—the absence of black people seemed natural, not the result of deliberate policy. But the policy often persisted, and for the same reason: It’s natural to be suspicious of people who obviously don’t belong... and to call the police, just in case.
For much more about the history and legacy of sundown towns, I highly recommend James W. Loewen’s book on the subject.