True, they could send a land-based army west and not stop until they get to Ireland and Cape Town.
<Lots of extra cannon fodder too.>
South would be more problematic because a billion Indians and sundry Indonesians/Moslems would get stroppy. Even Russia could make quite a mess back in Beijing so going west might not be all that simple either. Flying or sailing east would be hopeless too with Predator drones flying out of various countries, Hawaii, California, Oregon, and off aircraft carriers shooting them down by the million. North would be doable into Mongolia and Russia, but by 2020, with reglaciation looming, that's not going to be a good place to be. It would probably be easier to just buy the north with spare US$. Louisiana and Alaska were sold, Alaska by Russia.
While there's quiet at home, they can use those hordes to keep the rest suppressed. The main reason for conquests of times gone by was that there was simply nothing for the young men to do at home, other than plot to take over themselves. So the spare males had to be got rid of somehow. "Okay you guys, there are evil-doers just over the horizon. Lots of girls too. Spare land and glory. Here's a sword. Head on over there because those guys are planning on attacking and we have to get in first."
The chiefs over the horizon were saying the same thing.
The spare young men met on the battlefields and various problems were solved. If the conquest succeeded, and didn't just end in stale-mate, the territory got bigger and the tribe tougher. If there was stale mate, the breeding programmes would continue for another few decades to get the numbers up again and they would have a rematch.
These days, that whole economic drive has been supplanted with globalized economics and money to be made at home assembling iPhones or learning how to do software in Bangalore, or install fibre in Angola. I hope.
CDMA has delivered phragmented photons around the world, suffusing people everywhere with peace, light, harmony, happiness, health, prosperity, longevity, fun and love. They are in a Cyberspace trance. See Microsoft's advertisements which explain: youtube.com youtube.com They can't invade and conquer mobile Cyberspace. Mobile Cyberspace has invaded and conquered them.
Mqurice |