Wars are won or lost on a number of strategic factors: the greatest fighters, a well-equipped army, ferocious weaponry, and a well thought out ploy. Given these all played out on the plain of Troy another major element was integral in the final outcome of the war. Each side had allies, whereas the Akhaians were predominantly Greek, the Trojans bolstered their numbers from neighbouring states, empires with whom they had trade treaties.
An ally is:
• A state formally cooperating with another for a military or other purpose.
Ally something to/with
• Combine or unite a resource or commodity with (another) for mutual benefit.