[pear01]

It's also rare to just "discover" an entire continent that is basically free for the taking since Europeans annihilated native populations through disease and technological superiority.

Much of what makes America unique is tied to this essentially once in a generation event that will never happen again on this planet, a contingent confluence of Earth's parallel geographic and biological evolution... it's fairly easy to rebel or become a superpower when other powers have to contend with peer conflicts right on their borders. A break with England was inevitable why take orders from people an ocean away in the age of sail?

[BLKNSLVR]

That's one of the core plot points in The Mars Trilogy - Why take orders from people on another planet in the age of sub-light-speed space travel?

[ABCLAW]

It's worse than that; within a few generations our linguistic and biological systems will begin to diverge under conditions with little cross-pollination and different selective pressures. We will become aliens in the sci-fi sense very rapidly if we attempt to create a foundation-like diaspora of settlements.