Diversity is a positive in military terms, to a limited extent. Imagine a nation only having an air force, no army, navy or marines? Ancient Macedon is the best example, as the Macedonian army, which combined barbarian infantry, indigenous phallangites, Greek-style hoplites, and Greek and Persian style cavalry, could slaughter Persians, barbarians and Greeks alike as they had the same strengths as each but were able to make up for the weakness of each weapon type by their diversity
However, this diversity of weapon type and unit loyalty—the foot grunts hated the rich horsemen and they all despised the Agrianian mercenaries—and the fact that they had the same overall belief, that they were a combined arms team and that they would win, translated into a huge morale bonus.
Toward this end they put themselves at the command of an alpha male, behaving essentially like a football team.
Which brings us to cohesion, which is the glue of combat in groups larger than two!
You probably watch either baseball or football or basketball.
Who would win:
The Pro-bowl winner or the Superbowl winner?
The Allstar game Winner or the World Series Victor?
The Olympic Dream Team or Michael Jordans’ Chicago Bulls, or Jim Byrd’s Celtics, Or…you get the idea.
Historically "all-star terms" have failed miserably to reflect the sum of their component talents because they lacked cohesion.
When you get groups together for the purpose of getting anything done, than any group greater than two requires a common focus. The idea of the group and a commitment to cohesive action on the part of very different classes of athletes gets results, gets the W. Thing of an offensive lineman and a quarter back. These men are physical and mental opposites, yet they work together towards a common goal. Where diversity gets you in trouble is when the goals of the component parts of a team, army or society diverge radically.
This is why the Romans beat the Macedonian-style mercenary armies with their one dimensional infantry-heavy legion—they had cohesion from 10 men to 10 legions.
Let me give you a scenario:
Three wrestlers who have lived together, and have all come in second at the Olympics, get into a fight with the best boxer, best wrestler and best karate guy in the world, who just met each other at a restaurant. Who do you think will win, considering the fact that the boxer knows nothing about wrestling, the karate guys knows less and the best wrestler can barely contain one of the three second-rate wrestlers?”
That’s right, my friend, the best wrester stays off his back while his boxer and karate friend—who he didn’t have time to explain sprawling to—get slammed to the pavement, and know he’s facing three wrestlers.
That’s what cohesion does for you in combat, overcomes excellence, diversity of equipment and skill-set and size.
Thirty years after Alexander’s death, the men who were his father’s foot companions were well into old age, but were still the most sought after unit in the mercenary world of the Diodachi, his quarrelsome successors. They were called the Silver Shields and were so effective that they had to be killed, and were.
So, Jorge, in terms of Third World to First World immigration, whether or not this is a good thing depends on your perspective. If you are a nationalist this is bad, as your nation will slowly tear apart and then burst at the internal seams. However, if you are a globalist and want to see one world government, than using diversity as a strategy to balkanize nations in order to form a higher global unity from the remains is most wise.