No change. America still had a federal system in 1880. No major government initiatives without a war like 1860 for the Homestead Act, and the Morris Act and the Transcontinental Railroad, etc. No real reason to conquer empty lands or buy them, either. Nothing left. Even Alaska seemed a dud in 1880 because we hadn't found the gold, let alone the copper and the oil.
In 1880 America was way too powerfull to be invaded, but way to weak to invade someplace else except Canada, and why bother? The British had pulled all their troops out when they realized that the US could protect them just as well and wasn't interested in invading Canada themselves.
This is because we culturally would have had to let the Canadians vote and their senators would have spent the next generation punishing whichever political party caused the invasion.
