What would happen if there was a massive disinterest from post-colonial US senate (if not outright hostility against) to expand westwards, so even if they had the oppotunity to expand into the void of sparsely settled areas they didn't do it? Say that the disinterest was due to concerns about having relatively less power in how to rule the country, ending up expanding to the degree that the conquered areas would end up ruling, and concerns (realistic or not) that they would invite a coalition of european nations with colonies around them (Spain, France and Britain) to argee to put them in their place before resuming business as usual.