Let's assume that the Louisiana Territory is taken by Britain from France. Let's also assume that Britain and the US have friendly relations with each other as they cooperate over joint-ownership of the river.
How would no Manifest Destiny across the continent affect American culture?
With no access to the Pacific but a new land border to the west, would the US military be larger or smaller than OTL?
What effect would this have on slavery? Could there still be a civil war?
How would this affect the development of American cities? I assume that Chicago in TTL would be far less significant than in OTL.
How would this impact immigration? Is it possible for the US of TTL to attain the same population as the US of OTL, or would the population be much smaller?
How would this affect America's position on the world stage? Assuming it still develops into an industrialized great power, would it try to project its influence across the globe or would it remain isolationist?