After reaching North America, humans migrated to South America.
Physical geography focuses on natural processes of the earth, including climate and plate tectonics, whereas human geography studies the effect and behavior of humans and how they relate to the physical world. The two fields of geography are interrelated.
An anthropoid; this should be classified as biology not geography
A biggie: the transcontinental railroad. Because it would economically improve wherever it was, both the North and the South competed for the railroad to be in their respective territory, evidenced by the Kansas-Nebraska Act and the Gadsen Purchase and induction of California as a free state in 1860.
In addition: people could get land cheap because it was abundant and might leave to start afresh economically.
There's other stuff I can't remember as clearly, but there's a little and I hope it helps :)
