Quite a different situation. An empire is when you go to a populated place and extract wealth from the people who live there. That’s not what manifest destiny was. America expanded into land that was sparsely populated by natives americans and mexico who had no wealth to extract.
"America expanded into land that was sparsely populated"
What does this remind you of?
> expanded into land that was sparsely populated
Yes, that’s exactly the situation that results in highest income/wealth per capita. As long as that land can be utilized productively.