Spatial and Temporal Considerations of the Achaemenids and Greeks

I don't have the full story yet of what types of resource flows were involved in the back-and-forth struggle of the Achaemenid empire and the Greeks, but one issue that does seem to come up repeatedly is the presence of resources like timber and pitch in regions like Macedonia and other parts of the Balkans, which figured prominently in ship building in the ancient world. 

It would make sense that regions such as these would become contentious in terms of who is controlling them and the resources that are coming out of them. You need a hell of a lot of timber for those larger ships, and if you are looking to be a major player in maritime trade and warfare - which has been a necessity for the rapid movement of large quantities of resources for thousands of years - you better have a healthy supply. And those really large, healthy groves only grow in certain places.