>once Northern America was settled, the US established and the conflicts with Natives and the Brits resolved, all you had was the Civil War

As that list shows, that's not how things happened. There were major wars with the Native Americans all throughout the 19th century.

If for some reason you only want to include wars with Europeans and European colonies (I have no idea why you would though), the Mexican-American war, and the Spanish-American war are the big ones you missed. The War of 1812 was also another big war after the US had previously resolved our conflict with the British.

There were tons of other smaller skirmishes in North America. The Patriot War, the Aroostook War, the Reform War, the Cortina Troubles, the Utah War etc.

>once Northern America was settled

You can't even begin to say "once North America was settled" until the end of the 19th century.