Look at historical military alliances. Like, in WWI or WWII, nations had to decide whether to go at war alone for quick gains (chasing hares) or ally with others for larger objectives (hunting stags). The outcome depended heavily on trust in allies' commitments.

I think a big thing to consider is how the Roman military was a reflection of their society and politics. In the early Republic, soldiers were essentially citizen-farmers, right? So tactics were built around this idea of short campaigns close to home. But later, as the empire grew, you needed …