Speculation is that the iron wielding Hittites beat the bronze age armies they encountered because their iron spears and swords were superior to the bronze age weapons. I used to think this also until I saw reproductions of an iron and bronze sword strike each other and the bronze weapon held its own.

What probably did happen is that bronze was expensive and to maintain an army of bronze using warriors was expensive so bronze age armies tended to be small. The introduction of cheap iron means the Hittites could arm more of their people with the weapon and thus overwhelm the bronze wielding (and thus smaller sized armies).

I wonder if I should finally get my PhD on this?