The Social War, unfortunately, is not documented fully, and the lack of primary information other than books like Civil Wars by Appian makes it difficult to fully appreciate this political and military event that led to the unification of Italy and Rome. Despite the limited primary resources, the Social War was a major turning point in Roman history. It was also a policy change that significantly increased Roman military strength, a strategic shift that would have far-reaching implications.  Occurring between 90 and 88 BCE, the Social War is not classified as a civil war because it occurred between two allies and not citizens of the same country.

This conflict occurred primarily due to Rome recruitment of soldiers who were not Roman citizens.  Particularly the Samnites and Marsi people who comprised most of the Roman army as they defeated the Carthaginians. The Marsi and Samnites, Italic people, were not granted citizenship rights by the Romans, although previous campaigns resulted in citizenship, but not for the Italic. As a result, the Italic people represented a threat to the Romans.

Unfortunately for the Romans, the Italic army was comprised of soldiers who fought for the Romans, enjoyed the same training and technology as the Romans, and held the advantage due to Roman political distrust of Gaius Marius, the Roman general. Military engagements occurred in the North and South, with Lucius Cornelius Sulla commanding the Southern military and Pompeius Strabo in the North. However, the northern and southern campaigns gave the Romans a distinct advantage; they ended with a decree passed by Lucius Caesar, allowing citizenship to any Italic soldiers who either did not participate or capitulated when commanded.

The end of the Social War resulted not only in unifying Rome and Italy but also ended the devastation and economic hardships during the conflict. Resulting citizenship dramatically increased the Roman population and aided in future military campaigns. 

Personally, I had not heard of the Social War, but it does present an interesting challenge for policy on unified nations. The Social War increased the Roman population and a tertiary search yielded no information on any similar military conflicts between allies and the demand for citizenship.

Salmon, E. T. “The Cause of the Social War.” Phoenix 16, no. 2 (1962): 107–19. https://doi.org/10.2307/1086945.