Alexander of Macedon, more widely known as Alexander the Great, is one of history’s most famous conquerors. Many historians, poets, and writers have been mesmerized by his conquests. The enthralling images of Alexander’s actions has built an everlasting romantic impression of the man.

But while most talk of his invasions and exploits, you never really hear or read why he invaded the mighty Persian Empire in 335 BCE in the first place.

The Roman historian Arrian tells us that Alexander set out to conquer Persia as an act of revenge for past wrongs. Alexander addresses this in his letter to Darius stating: “Your ancestors came into Macedonia and the rest of Greece and treated us ill, without any previous injury from us. I, having been appointed commander and chief of the Greek, and wishing to take revenge on the Persians, crossed over into Asia, hostilities being begun by you.”

But was it really all about revenge or was there something more to it… is it possible that Alexander just needed money?

It’s true that most books discussing Alexander’s invasion of Persia say revenge was the main motivator, payback for the Greco-Persian Wars of the past. All the same, it is rather odd that Alexander would all of the sudden decide to mount his horse and lead his army into the lands of Persia, especially since the war had been over for more than one-hundred years.

However, there is another passage that our Roman historian Arrian provides. Apparently, Alexander gave a speech at Opis in 324 BCE when his men mutinied for a second time, and in it he furnishes us with an interesting statement as to why he declared war on Persia, that being money.

“I inherited from my father a few gold and silver cups, and less than 60 talents in the treasury; Philip had debts amounting to 500 talents, and I raised a loan of a further 800.”

But there is a bit of backstory first. See, Alexander’s father Philip had already set his eyes on Persia and was preparing an invasion force, but was assassinated before he could carry out his objective. With his death, Alexander was left with a semi-professional army, a fighting force paid directly by the king himself.

In order for Alexander to afford this army, he had to either disband a portion of it to save money, risking much in doing so, or go on the march to salvage his kingdom. In the end, he choose to save his kingdom at another empire’s expense. Essentially, Alexander needed to pay the bills by conquering and confiscating Persia. It was a risky investment to say the least.

As the early 20th century intellectual Randolph Bourne once stated: “War is the health of the state.” Indeed it was, for Alexander was the state and war was his business. Therefore, revenge was evidently not Alexander’s motivator.

Instead, revenge was just a facade to expand political means in order to fill his coffers. Once Alexander had enough means, and his treasuries overflowed, he could continue the unrelenting, perpetual war until the entire known world was his.