This is about more oil mining, about Trump appeasing to his oil friends, considering Greenland very likely has a substantial quantity of it.
Rather these invasions appear to be the pet projects of neo-imperialist advisors in the government who see national growth as a zero sum game, a Starcraft-esque race for a finite set of resources where powerful countries can generate wealth only by using their power to steal from others. In Steven Miller's own words: "[The world] is governed by force, [is] governed by power. These are the iron laws of the world since the beginning of time."
Instead he will soon be remembered as the worst US president ever - even after his first term he was already third-worst in most rankings and his second term is orders of magnitude worse.
He will be remembered as the president that destroyed the constitution, destroyed America's formidable power projection, the president that destroyed 60 year long alliances, the president that was unimaginably corrupt. I just hope that American school books will also contain the verdict.