"...Inner vs. Outer Rims
In the last 10,000 years, the world's most developed societies have almost always been in the band of latitudes that Mackinder called Eurasia's "inner rim," running from the Mediterranean to China. Farming was invented in this area, with the Middle East leading the way around 9500 B.C. and the rest of the inner rim following its example over the next several thousand years. Along with farming came cities and governments, which most parts of the inner rim had developed by 500 B.C. Two hundred and fifty years later, the world's first multiethnic empires comprising tens of millions of subjects controlled most of the inner rim.
Because ancient empires could not project their power very far, at any one time the inner rim tended to have four or five regional hegemons, jostling with each other but rarely extending their power into what Mackinder called Eurasia's "outer rim," facing toward the oceans, or its "heartland," far from the seas. However, because Eurasia's inner rim held 75 percent of the world's population and 90 percent of its wealth, its imperial rivalries became the most significant issues in global geopolitics.
The planet's balance of power began to change around 1000 B.C., when pastoral nomads on the steppes — the arid, treeless grasslands running from Manchuria to Hungary — first bred horses able to carry riders for long distances. These horsemen in the Eurasian heartland, far more mobile than the armies of the inner rim empires, were able to plunder almost at will and then gallop away before the imperial infantry could respond...."
https://www.stratfor.com/weekly/iranian-power-not-inevitable