The socii (/ˈsoʊʃiaɪ/ in English; ""allies"") were the autonomous tribes and city-states of the Italian Peninsula in permanent military alliance with the Roman Republic until the Social War of 91–88 BC. After this conflict, all Rome's peninsular Italian allies were awarded Roman citizenship and their territories incorporated in the Roman state. The Romans themselves referred to their confederates as the socii Latini (""Latin allies""), although most were not members of the Latin tribe strictly speaking, but members of various other Italian tribes and city-states. In everyday usage, the word socius /ˈsoʊʃəs/ could mean ""associate"" or ""partner"" in general.The alliance had its origin in the foedus Cassianum (""Treaty of Cassius"", 493 BC) signed by the fledgling Roman republic with its neighbouring Latin city-states shortly after the overthrow of the Roman monarchy in 510 BC. This provided for mutual defence by the two parties on the basis of an equal contribution to the annual military levy, which was probably under Roman overall command. The terms of the treaty were probably more acceptable to the Latins than the previous type of Roman hegemony, that of the Tarquin kings, as the latter had probably required the payment of tribute and not a simple military obligation.The foedus served as the basic template for Rome's settlement with the large array of tribes and city-states of the whole Italian peninsula that it subjugated during the period 338–264 BC. At the start of this period, the original Latins were mostly granted Roman citizenship. But the terms of the foedus was extended to about 150 other tribes and city-states. When a state was defeated, a part of its territory would be annexed by Rome to provide land for Roman/Latin colonists. The latter, although Roman citizens, were required to give up their citizen rights on joining a colony, and accept the status of socii. This was in order that Latin colonies could act as ""watchdogs"" on the other socii in the allied military formations, the alae. The defeated state would be allowed to keep the rest of its territory in return for binding itself to Rome with a perpetual treaty of military alliance. This would require the ally to ""have the same friends and enemies as Rome"", effectively prohibiting war against other socii and surrendering foreign policy to Rome. Beyond this, the central, and in most cases sole, obligation on the ally to contribute to the confederate army, on demand, a number of fully equipped troops up to a specified maximum each year, to serve under Roman command.The Roman military alliance had fully evolved by 264 BC and remained for 200 years the basis of Roman military organisation. From 338 BC to 88 BC, Roman legions were invariably accompanied on campaign by roughly the same numbers of allied troops organised into two units called alae (literally: ""wings"", as allied troops would always be posted on the flanks of the Roman battle-line, with the Roman legions holding the centre). 75% of a normal consular army's cavalry was supplied by the Italian socii. Although the socii provided around half the levies raised by Rome in any given year, they had no say in how those troops were used. Foreign policy and war were matters exclusively in the hands of the Roman Consuls and the Roman Senate. The latter, in turn, was a narrow, self-perpetuating 300-strong clique of wealthy men who monopolised power in the Roman republic, despite the theoretical sovereignty of the Roman people.Despite the loss of independence and heavy military obligations, the system provided substantial benefits for the socii. Most importantly, they were freed from the constant threat of aggression from their neighbours that had existed in the anarchic centuries prior to the imposition of the pax Romana. In addition, the Roman alliance protected the Italian peninsula from external invasion, such as the periodic and devastating incursions of Gauls from the Po Valley. Although no longer in control of war and foreign policy, each socius remained otherwise fully autonomous, with its own laws, system of government, coinage and language. Moreover, the military burden was only half that shouldered by Roman citizens, as the latter numbered only about half the population of the socii, but provided around half the total levies. Despite this, allied troops were allowed to share war booty on a 50–50 basis with Romans.Despite these benefits, many socii rebelled against the alliance whenever the opportunity arose. The best opportunities were provided by the invasions of Italy by the Greek king Pyrrhus in 281–75 BC and by the Carthaginian general Hannibal in 218–03 BC. During these, many socii joined the invaders, mostly Oscan-speakers of southern Italy, most prominently the Samnite tribes, who were Rome's most implacable enemy. At the same time, however, many socii remained loyal, motivated primarily by antagonisms with neighbouring rebels. Even after Rome's disaster at the Battle of Cannae (216 BC), over half the socii (by population) did not defect and Rome's military alliance was ultimately victorious.In the century succeeding Hannibal's War (201–91 BC), Italy was no longer threatened by external invasion (save by the occasional Gallic or Germanic horde) and Rome and her allies embarked on aggressive expansion overseas, in Spain, Africa and the Balkans. Despite the fact that the alliance was no longer acting defensively, there was virtually no protest from the socii, most likely because the latter benefited equally in the enormous amounts of war booty yielded by these campaigns.But, beneath the surface, resentment was building among the socii about their second-class status as peregrini i.e. non-citizens (except for the Latin colonists, who could regain their citizenship by moving to Roman territory). The Roman military confederation now became a victim of its own success in forging a united nation out of the patchwork of ethnicities and states. The socii rebelled en masse, including many that had remained steadfast in the past, launching the so-called Social War. But, unlike on previous occasions, their aim was to join the Roman state as equal citizens, not to secede from it. Although the socii were defeated on the battlefield, they gained their main demand. By the end of the war in 88 BC, all inhabitants of peninsular Italy had been granted the right to apply for Roman citizenship.