> How do you know it was simply a matter of more land leading to more chance of civilization appearing there?
Human brains are energy intensive. More land means higher likelihood of arable land, more livestock and so better nutrition. It also makes your land more valuable to invaders, which leads to people organising to protect their land, and innovating weaponry, tactics, etc.
Certainly it might have taken some special circumstances like you said, but when there are perfectly plausible reasons suggesting the contrary, there seems little reason to give speculative possibilities much attention until there's evidence.
Human brains are energy intensive. More land means higher likelihood of arable land, more livestock and so better nutrition. It also makes your land more valuable to invaders, which leads to people organising to protect their land, and innovating weaponry, tactics, etc.
Certainly it might have taken some special circumstances like you said, but when there are perfectly plausible reasons suggesting the contrary, there seems little reason to give speculative possibilities much attention until there's evidence.