Rome built its empire of the back of soldier-farmers.
We tend to think on the professional armies of the Late Republic and Empire as representative of the Roman legions at their best, the secret behind of Roman success - often overlooking the dynamic, stubborn, multicultural and multi-ethnic character of said armies and their society overall as what separated Rome from other "great conquerors". However, a professional soldier class only emerged after Rome became a super-power, an answer to the demands of their expanding empire, the abysmal increase of the wealth gap and the changes on their relationship with allies. The army that actually built the empire was of a very different sort.
During most of the history of the Republic, military service was associated with one's own wealth. As such, war was the domain of the landowner; the urban poor, still not as relevant as during later centuries, was mostly relegated to auxiliary military roles or served in positions that did not require much money, such as crewing the nascent Roman navy or maintaining supply lines and markets open. Curiously, such military organization also kept the poorest from attaining political glory or sharing the loot.
In a way, this was almost a reversal of the almost cliche lifepath of the Late Republican/Imperial Legionary: urban poor or foreign youth, serve on the legions for a few decades, then be rewarded with lands/citizenship and be settled on some newfound colony. Our typical Republican legionary and their family subsists from the land, is a citizen of Rome or an ally and wages war to protect the interests of the Senate and defend the Republic, being rewarded with a share of the loot and a chance for social and political advancement.
This dictated that the pace of the war was set by the rhythm of the seasons. Since the backbone of the army were also the farmers that fed Rome, year-long campaigns were nearly impossible, and any overseas military endeavors would also mean famine, loss of lands to larger holders that can handle economical stress better and price gouging.
During the time of Heroes of the Republic, the soldier-farmer still rules the battlefield; however, the seeds of change have already been planted. The acquisition of the fertile Sicilia and Sardinia provinces from Carthage radically changed the way Rome feed itself and their allies, allowing the Senate to wage war across the Adriatic Sea and subjugate the pirate nations of Illyria. Most curious of all, was the declaration that this war was waged to protect their now sea-bound lifeblood. As the Barcids threaten from Iberia and the network of Roman allies expand East, how far from the fields can these farmers go?