More efficient trade, the rise of Atlanta, and fewer cities built along rivers can all be attributed to what?

The development of the Railroad.

Explanation:

The things you describe can all be given thanks to the development and creation of complex railroad systems that dominated what was modern transportation from the mid-1800's through early-1900's.

Hope this helped, have a great day either way!

it would be

china unilaterally claims the entire south china sea as sovereign territory, then builds artificial islands to bolster its claim. it suddenly activates an air defense identification zone over the east china sea, and threatens to down any aircraft that does not report its position. it builds roads into indian territory, then redraws the maps to show that it is actually chinese territory. the people's republic under president xi jinping is quickly becoming the bully of asia.