The expansion of the Roman city in Italy and later in the Mediterranean, from the early 5th to the late 3rd century BC, results in a growing number of military alliances with various communities which nonetheless remain independent. This specific union - called "societas" by the Latin people - is traditionally referred to as one of the tools used by the Urbs to assert its supremacy, insofar as it allows the rallying of its partners' forces. However the representations on both sides keep parity and reciprocity as principles of paramount importance. Such is revealed by the observation of not only the political and diplomatic conditions of their negotiations, but also of the terms which seal the agreements - even more so regarding the "foedus sociale" - and of the diplomatic events they lead to. The alliance indeed specifies that each signatory shall be recognized as a community with its own military forces, and commits them to provide mutual assistance. The study of the relations which Rome established - first with the Latins in the 5th century through the "foedus Cassianum", and later with many Italian or peoples overseas - points at the duty of defence being the core of military cooperation. Hence the Romans using it as a figment of propaganda, such as the affirmation of them being the most trustworthy guardians of the 3rd century Italia. However both extra and peninsular partners still express a vivid concern regarding the ideals which are usually associated the military alliances. The Second Punic war clearly highlights this ideological bone of contention, and seriously jeopardizes the Roman system of alliances. It is only their hard-won victory over Carthage that allows them to rule over the terms of this relation.
