I've delved into a book called Marathon by Richard A. Billows. Its a good read but he discusses something I've not run across before...though it may be common in Greek Historiography. The early Greeks fought like most ancient peoples, light armor, spears, javelins, slings etc. Only the aristocrats were heavily armed and these fought in small groups. These early city states were ruled by the aristocracy, those with the money to create weapons and armor.

Just previous to the age of tyrants Greece began to expand economically. Trade facilitated alot of this, followed by the creation of finished goods...pottery etc. Money flowed into the cities, tradesmen became wealthy. The age of tyrans rolls in, lasting about 30 odd years and spread through many states. Then the hoplite enters the scene. We don't know if one led to the other or if they were unrelated, but the ability of the small tradesman to arm himself with heavy weapons changed the nature of Greek society. Within a few decades citizen bodies were running the various states.

So one theory is that the ability of the small land holder, tradesman, etc to arm himself led to the end of the rule of the Tyrants. It also led to the creation of the Hoplite soldiery, that went on to defeat the Persian Empire on numerous occasions.

That's probably a gross oversimplifications, but food for thought.