The Persian Empire at the time of its wars with Greece is estimated to have had a population of 50 million people. Greece had around 500,000. Persia therefore outnumbered Greece 100:1. Yet it was Greece consistently defeating its much larger rival, and ultimately destroying it at the hands of Alexander (okay Macedonian, but Greek-influenced). Usually this is simply explained away as "the Greek armies were far superior" - but why? Persia had a long and glorious military tradition and had far more resources for vital elements such as archery and cavalry, even some exotic additions such as camels and elephants.

So here is a theory. The Greeks were divided into city-states that were almost constantly at war. Under regular circumstances such internecine strife would be profoundly debilitating. Probably because of that threat, the Greeks developed an honourable code of war that permitted them to fight each other without mutual destruction. Heavily armoured infantry clashed and the goal was to drive the opposing army from the field rather than massacring it. Afterwards there would acknowledgement of victory with exchange of the dead and a treaty. The battle was hard but won or lost with relatively few casualties. This meant that the Greeks were essentially performing non-deadly war exercises for decades, even centuries.

But in Persia, internecine warfare was often between rival claimants for the throne. With the need to eliminate all opposition not just to restore peace but to make an example for anyone else thinking of revolt later, wars were far deadlier and therefore both rarer and more debilitating.

What Philip II and then his son Alexander achieved was capturing the best of both worlds: the traditional Greek skill of defence, but adding greater offence with deadlier phalanx and cavalry. Now the army was not only extremely hardy but an instrument of extermination.

So Alexander's conquests came from centuries of non-lethal rivalry among the Greeks suddenly turned outwards. The same can be said of the Mongol and Arab conquests, which also took on and defeated far greater powers.

The Persian Empire at the time of its wars with Greece is estimated to have had a population of 50 million people. Greece had around 500,000. Persia therefore outnumbered Greece 100:1. Yet it was Greece consistently defeating its much larger rival, and ultimately destroying it at the hands of Alexander (okay Macedonian, but Greek-influenced). Usually this is simply explained away as "the Greek armies were far superior" - but why? Persia had a long and glorious military tradition and had far more resources for vital elements such as archery and cavalry, even some exotic additions such as camels and elephants.

So here is a theory. The Greeks were divided into city-states that were almost constantly at war. Under regular circumstances such internecine strife would be profoundly debilitating. Probably because of that threat, the Greeks developed an honourable code of war that permitted them to fight each other without mutual destruction. Heavily armoured infantry clashed and the goal was to drive the opposing army from the field rather than massacring it. Afterwards there would acknowledgement of victory with exchange of the dead and a treaty. The battle was hard but won or lost with relatively few casualties. This meant that the Greeks were essentially performing non-deadly war exercises for decades, even centuries.

But in Persia, internecine warfare was often between rival claimants for the throne. With the need to eliminate all opposition not just to restore peace but to make an example for anyone else thinking of revolt later, wars were far deadlier and therefore both rarer and more debilitating.

What Philip II and then his son Alexander achieved was capturing the best of both worlds: the traditional Greek skill of defence, but adding greater offence with deadlier phalanx and cavalry. Now the army was not only extremely hardy but an instrument of extermination.

So Alexander's conquests came from centuries of non-lethal rivalry among the Greeks suddenly turned outwards. The same can be said of the Mongol and Arab conquests, which also took on and defeated far greater powers.