According to The Warmth of Other Suns: The Epic Story of America's Great Migration by Isabel Wilkerson, the migration of African Americans from the South was both necessary and intimidating. This tension is the crux of the problem she documents, through the lives of three families, in this book. The "situational complexity" you ask about, at least in part, is the tension between their ambitions, hopes, and dreams and what soon became their reality.
From the early years of the twentieth century to well past its middle age, nearly every black family in the American South, which meant nearly every black family in America, had a decision to make. There were sharecroppers losing at settlement. Typists wanting to work in an office. Yard boys scared that a single gesture near the planter’s wife could leave them hanging from an oak tree. They were all stuck in a caste system as hard and unyielding as the red Georgia clay, and they each had a decision before them. In this they were not unlike who ever longed to cross the Atlantic or the Rio Grande.
Six million African Americans worked their way from the South to the North. While they escaped one set of problems, they encountered many new ones.
The North was facing a labor shortage and African Americans from the South were a source of cheap labor. It seems like that would have been a perfect match; however, finding work was not easy and the jobs they found (baggage handler, nurse’s aide, factory worker) often relegated them to life in the ghetto.
They struggled with such mundane issues as not being able to understand the local dialect and such awful realities as drugs, teenage pregnancy, and the other dangers of living in poverty. Racism and prejudice, of course, were still prevalent in the North, and the hopes and dreams of these families (representative of all who migrated) were certainly not realized, at least not for generations.
One of the three families she writes about, Robert Foster, was able to achieve success relatively quickly, but it was exceptionally hard for him and he was continually haunted by the need to prove himself and justify his success to others. Sp, even when one of the three families in this story achieved his dream, he was unable to escape his sense of inferiority which he learned and lived in the South.
Not everything about their migration was terrible, however, and those who chose to move set a new path and direction for the generations that followed. Some of the first to come were even able, eventually, to go back; this freedom to live wherever and be whatever they wanted was a crowning achievement for those who were once living without any hope of real freedom.
The most important aspect of this story is the courage it took them to leave.
Perhaps it is not a question of whether the migrants brought good or ill to the cities they fled to or were pushed or pulled to their destinations, but a question of how they summoned the courage to leave in the first place or how they found the will to press beyond the forces against them and the faith in a country that had rejected them for so long.
Like everyone who longs for freedom but does not have it, they had to take action. The phenomenon known as the Great Migration was not a planned and organized event. It was simply people who wanted more, deciding to seek out opportunities to get it.
They did what human beings looking for freedom, throughout history, have often done. They left.