"Unite under one flag..." is not gonna happen. Last time anything really important like that was the United Nations "police action" in Korea. How did that go? And it is still an unfinished one, 66 years after the shooting stopped.
Oops, I forgot the Gulf War #1, which did nothing about Sadam. Had to have Gulf War #2, which went on for a decade or so. And Afghanistan conflict? Deep into its second decade. Syria is up to 7 years, and will last longer.
So don't expect any time soon that people on this planet will get together to do anything about stuff on a different planet.
Try reading the "Club of Rome" reports on economy, ecology, demographics that have had accurate predictions for about 40 years. You will see that humans will be lucky even to survive past 2050 on just this planet, much less any other.