The Mongols may not have had cities (besides Karakorum, the capital). However, by the time Genghis Khan's conquests were under way they had a written alphabet, a very highly organized military structure, a complex legal code, freedom of religion, and a postal system that was unrivaled until the Pony Express was established in the US. They were generally far more sophisticated than you give them credit for and their system of warfare was more than just 'tribal'. Sure, they used hit and run tactics, but a great deal of logistics and organization is required to besiege cities.
Sacking cities and killing the inhabitants was nothing new. The Crusaders did it at the end of the siege of Acre during the 3rd crusade. Khan actually gave the cities he attacked a chance to surrender and be spared.
Also, the term "barbarian" is loose, vague, and sometimes downright irresponsible when talking about history. Different cultures have viewed others as barbarians throughout history. Unless we're talking about one of these specific cases (such as the Greeks calling those north of them barbarians, or the ancient Chinese calling everyone around them that) it's a meaningless term. Would you call tying peasants to the land and severely limiting their rights and freedom to even move around a barbaric practice? Or is it just cruel or unfair?
I truly believe that a civilised society does not fall apart after the death of one man.
The Mongolian Empire was an incredible military achievement, but it was only an Empire in terms of conquest - it wasn't an Empire in terms of sustained society (like the Roman, Byzantine, or British Empires). The guy at the top dies, and the whole thing falls apart? That's not really a 'civilised society'.
Ancient Greece was a collection of societies that shared Greek culture. "Alexander's Greece" lasted only a few years and was hardly a society unto itself - it was another example of an empire-by-conquest. The guy at the top dies, and it all falls apart again.
Unless you're trying to tell me that Alexander turned the people all the way to the Indus into greek culture adherents, no, Alexander's empire wasn't a society.
It's important to note here that Alexander created a short-lived empire - he did not create the society we think of as 'ancient greek'. That pre-existed him quite considerably in greece. And just because he gathered Perseopolis into his fold doesn't make the society there 'greek'.
But there was still a civilized Greek culture that formed the backbone of Alexander's organization and army, even if all the conquests weren't assimilated into the same civilization.
"Yes, of course. It came to existence when Ghengis Khan united nomadic tribes"
The original poster posited that Ghengis Khan's activities birthed the society. Alexander's activities did nothing like this - the society was already there, and greek culture was fairly widespread to begin with, though perhaps not in the direction of the Indus. When Alexander died, the Greeks didn't fade away to become background players again - they were a powerful political and especially social force for centuries to come... largely in the opposite direction to Alexander's conquests.
Alexander was an incredible conquerer, but he did not make nor break Greek civilised society.
I'm going back farther than that--to gizmo's contention that civilized societies don't engage in warfare. spindrift made the counterpoint that "only civilized societies can...engage in organized warfare", to which Genghis Khan may or may not be a counterexample, but Alexander's Greece is every bit as much of a counterexample to gizmo's argument.
Sacking cities and killing the inhabitants was nothing new. The Crusaders did it at the end of the siege of Acre during the 3rd crusade. Khan actually gave the cities he attacked a chance to surrender and be spared.
Also, the term "barbarian" is loose, vague, and sometimes downright irresponsible when talking about history. Different cultures have viewed others as barbarians throughout history. Unless we're talking about one of these specific cases (such as the Greeks calling those north of them barbarians, or the ancient Chinese calling everyone around them that) it's a meaningless term. Would you call tying peasants to the land and severely limiting their rights and freedom to even move around a barbaric practice? Or is it just cruel or unfair?