Why did americans show little interest in expanding their nation's territory and international power in years immediately following the civil war

These were the big years of settlement in the west.

Before the Civil War, the Southern states were busy finding more land to plant cotton and tobacco. They had used land very inefficiently, so from colonial times rich Southern planters were always looking for new land, and the richest people in the country were land speculators--one of the richest being ol' George Washington himself.

After slavery was abolished, it changed the way we looked at expansion. The old plantation system was dead, so now all the territories to the West were being settled by small farmers. Towns were being built, railroads were expanding, new states being admitted to the Union. When the West was opened up to homesteading, after the Civil War, politicians in Washington though it would take 300 years to fill out all that land, but it turned out to take only about 1/10 that long.

By the time of Teddy Roosevelt, all the western lands were 'full', so now we could turn our attention to acquisition of colonies, becoming an imperialistic world power, etc.