While millions of southern black Americans famously went 'up north' or 'out west' between 1895 and 1925, most stayed and had children within the broadly defined South.
They still moved about alright, many of them - but moved from state to state along the horizontally-lying Black Belt where Cotton had been King and the black population was the densest.
Similarly, while two million Jews left The Pale of the Russian Empire in the same period to flee the deadly anti-Jewish pogroms , most stayed and with a similarly high birthrates, maintained their same percentage of the - growing - Russian population.
It took first WWII's Holocaust and perhaps more importantly, decades of postwar communist-sanctioned anti-semitic abuse, to reduce the Jewish population of Russia from being a majority of the world's Jewish population at the end of the 19th century to today where Russian Jews are barely 1% of the world's Jews.
Contrast this to America's blacks, many of whom today are moving back to the same Deep South their parents and grandparents once fled to avoid government-sanctioned anti-black pogroms ...