Arguably the most important factor in the development of any group of people is geography. This is especially so in the ancient world where there was less technology (and ability) to alter geography.
The best way to proceed is by looking at a few examples. If you look a the ancient Greeks, their geography completely shaped them. First, there was no great river system that united them or allowed them to form a great kingdom. What contributed to this division was also the mountainous terrain. Greece is roughly 70% mountains. These mountains separated the cities. In light of these two points, the Greeks formed many cities without a centralized government. However, because they spoke the same language and shared customs, they still worked together. Their geography created a context of decentralized cooperation.
If we look at today, we can say that geography also plays an important role. Here is an example, countries with little natural resources, like South Korea, are forced to import natural resources. On the flip side, countries like Saudi Arabia, that sit on great oil reserves, can export their natural resources.
From these two examples, the geography of a land shapes the development of a people in profound ways.