What set the boundary for colonists along the appalachian mountains

1) union forces launched a surprise attack.

2) more confederate troops arrived by train.

3) union forces retreated.

the second significant cause of the great migration was the desire of black southerners to escape segregation, known euphemistically as jim crow. rural african american southerners believed that segregation - and racism and prejudice against blacks - was significantly less intense in the north.