The United States emerged as a leading world power after world war I due to the treaty of Versailles. This is my best answer. I hope this helps! :)
Depending on what you mean, it changed when the north saw that slavery was not just, and started goin on the attack on it. Which lead to the whole civil war of confederates vs the union
The great migration happened between 1916-1970 and was when 6 million African American were moved out of the Southern United States and to the urban Northwest, Midwest, and west
A unique property of stem cells is that they can divide and differentiate, meaning they can become specialized cells. Stem cells can specialize to gain a specific function, for example a stem cell can become a liver cell.