When you think about it, this is not that hard, so let me explain :)
When Greek citizens finally had cheap iron weapons (well, not all of them did, but those who could afford them were also more likely to buy them), this enabled them to have more independence and they could rely more on their "self-defence" capabillities, compared to earlier times, where the only group(s) of people who were able to exert power was the army or bands of mercenaries.
