Roman conquest of the Hernici
The Roman conquest of the Hernici, an ancient Italic people, took place during the 4th century BC. For most of the 5th century BC the Roman Republic had been allied with the other Latin states and the Hernici to successfully fend off the Aequi and the Volsci. In the early 4th century BC this alliance fell apart. A war fought between Rome and the Hernici in the years 366 - 358 BC ended in Roman victory and the submission of the Hernici. Rome also defeated a rebellion by some Hernician cities in 307 - 306 BC. The rebellious Hernici were incorporated directly into the Roman Republic while those who had stayed loyal retained their autonomy and nominal independence. In the course of the following century the Hernici became indistinguishable from their Latin and Roman neighbours and disappeared as a separate people.
The foedus Cassianum - 5th century BC
The ancient sources tell that in 486 BC the Hernici joined the foedus Cassianum, a mutual military alliance between the Latin cities with Rome as the leading partner. While the precise workings of the Latin League remains uncertain, its overall purpose seems clear. During the 5th century the Latins were threatened by invasion from the Aequi and the Volsci, as part of a larger pattern of Sabellian-speaking peoples migrating out of the Apennines and into the plains. Fighting is recorded against either the Aequi, the Volsci, or both, almost every year during the first half 5th century. This annual warfare would have been dominated by raids and counter-raids rather than the pitched battles described by the ancient sources. During the second half the 5th century the Latin-Hernician alliance appears to have stemmed the tide. The sources records the founding of several Roman colonies during this era, while mention of wars against the Aequi and Volsci become less frequent. At the same time this would lessen the need to maintain the alliance. This was especially true for Rome which after her conquest of Veii in 396 was clearly the most powerful state in Latium.
Defection of the Hernici - 380s BC
Livy writes that in 389, after a hundred years of loyal friendship, the Latins and Hernici defected from Rome in 389, after Rome had been sacked by the Gauls. Then in 386 and 385 Latin and Hernician men were found fighting for the Volsci.  Rome protested, and refused to hand back their Latin and Hernician prisoners, but did not declare war.
Livy viewed the sack of Rome by the Gauls as a grave disaster that encouraged Rome's neighbours to rise against her. Modern historians however believe the ancient historical tradition exaggerate the impact of the sack. Likewise they disagree with Livy's views that the Hernici defected from Rome; as Livy notes, no open warfare between Rome and the Hernici is recorded for this time period. Rather the military alliance between Rome and the Latins and Hernici appear to have been allowed to wither. This might have been a willed policy by Rome to free herself from treaty obligations and so gain wider freedom of action. But the Latins and the Hernici, no longer threatened by the Aequi and Volsci, could also have seized the opportunity of the Gallic Sack to abandon their alliance with an increasingly dominating Rome.  While it is possible that this led to some Latin and Hernician warriors fighting for the Volsci, these could also be inventions by Livy to provide a literary motif to his narrative.  Except for these doubtful notices then, no conflicts are recorded between Romans and Hernici until 366
The Hernician War 362 - 358
After some mostly peaceful years, the Romans in 362 went to war against the Hernici, starting a period of unprecedented successful warfare for the Romans. Livy provides the only narrative account for this Hernican War. In addition two triumphs and an ovation against the Hernici are recorded in the Fasti Triumphales.
Outbreak of the war
According to Livy in 366 it was reported in Rome that the Hernici had rebelled, but nothing was done to prevent any action from being taken by the plebeian consul. In 363 to ward off pestilence the Romans nominated L. Manlius Imperiosus dictator to perform the ancient ritual of "driving in the nail" at the temple of Jupiter Optimus Maximus. Manlius however attempted to use his appointment to secure command in the war against the Hernici, but faced with public resentment and resistance from the tribunes of the plebs he was forced to lay down his office.  After fetials had been sent to the Hernici to demand satisfaction without result, the Roman Assembly in 362 voted for war against the Hernici. L. Genucius Aventinensis became the first plebeian consul to command in war, but the Hernici caught Genucius in an ambush; the consul was killed and the Roman legions routed.
As usual Livy makes Rome the offended party, but Roman designs on Hernician land might well have been real cause of this war. The failed levy of L. Manlius is probably not historical, but has likely been invented as a motive for the famous prosecution of L. Manlius, traditionally dated to 362. 
Dictatorship of Appius Claudius Crassus
The surviving patrician consul, Q. Servilius Ahala, then nominated Appius Claudius Crassus as dictator. Pending the arrival of the dictator, C. Sulpicius Peticus assumed command of the Roman army. The Hernici had surrounded the Roman camp, but led by Sulpicius the Romans sortied and forced them to retreat. With the arrival of the dictator with fresh forces from Rome, the strength of the Roman army was doubled. On their side the Hernici called up all their men, and formed a special privileged unit of 3 200 picked men. The Romans and Hernici had camped on each side of a two miles broad plain, and the battle took place in the middle. When the Roman cavalry found they could not break the enemy lines by normal means, they dismounted and charged as infantry. They were countered by the special picked men of the Hernici.  After a hard struggle the Roman knight got the best of this contest and the Hernici were routed. The next day the Romans were delayed in attacking the Hernician camp by difficulty in obtaining favourable omens and consequently failed to take the camp before darkness broke off fighting. During the night the Hernici abandoned their camp and withdrew. Seeing the retreating Hernici pass by their walls the people of Signia sallied out and scattered them in flight. Roman casualties had been heavy, a quarter of their whole force, and a considerable number of their cavalry had fallen.
Livy's extended narrative of this campaign is full of standard annalistic features and very little of the detail provided can have been derived from authentic records. The first military command ever held by a plebeian consul and the subsequent dictatorship of the conservative patrician Appius Claudius ties Livy's account into the Struggle of the Orders. Because of this literary character of the episode, and the absence of a triumph for Appius Claudius in the Fasti Triumphales, some historians have rejected Appius Claudius' dictatorship. Oakley(1998) does not consider these arguments decisive, but believes the basic notice of a Roman victory against the Hernici in 362 to be historical, and perhaps also the dictatorship of Appius Claudius and the involvement of Signia as well.
Livy only provide brief narratives for the remaining years of the Hernician war, being more interested in the Gallic wars Rome was fighting at the same time. In 361 the Roman consuls invaded Hernician territory. Finding no enemy in the field, they attacked and took Ferentinum.  In 360 consul M. Fabius Ambustus received command of the war against the Hernici.  Fabius defeated the Hernici first in some minor battles and then in a major one where the Hernici attacked in full strength. For his victories Fabius entered the City of Rome in Ovation.  In 358 the Romans assigned command of the Hernician war to consul C. Plautius Proculus. The consul defeated the Hernici and reduced them to submission. The Pomptina and Publilia tribes were also formed that year.  The Fasti Triumphales records a triumph by consul C. Sulpicius Peticus against the Hernici in 361, the ovation of M. Fabius Ambustus in 360, which according to the Fasti took place on 5 September, and the triumph of consul C. Plautius Proculus in 358 which it dates to 15 May.
There are no particular reason to doubt the historicity of these Roman victories though it is unlikely that Livy's description of Fabius first winning several minor battles and then a major battle, perhaps a condensation of a longer account found in his sources, is derived from authentic records. In 358 the Latins renewed their alliance with Rome when Latium was threatened by invasion from the Gauls, fear of the Gauls might also have influenced the Hernici to accept a new treaty with Rome,  but the Hernici probably obtained less favourably terms than their old alliance.  Ferentinum is described as independent in 306, and so must have been handed back to the Hernici at some point, perhaps as part of the peace terms. Of the two Roman tribes created in 358, the Pomptina was evidently located in the Pomptine on territory Rome had taken from the Volsci. The location of the Publilia is less certain, modern historians generally locate it on territory taken from the Hernici, but it is possible that the Publilia was also located on former Volscian land.
Final rebellion of the Hernici 307-306
Towards the end of the Second Samnite War, in 307 BC, the Romans found a number of Hernician men among prisoners taken in battle against the Samnites. These were placed under guard in various Latin towns while the Romans investigated whether they had fought for the Samnites voluntarily or had been conscripted. In response part of the Hernici, under the leadership of the city of Anagnia, in 306 rose in rebellion, but were easily defeated by the Romans that same year. As punishment Anagnia and the other towns that had rebelled were annexed into the Roman Republic, their people becoming civitas sine suffragio. Aletrium, Ferentinum and Verulae were allowed to retain their autonomy and enjoy similar political rights as the Latins.
- Livy, vi.2.3-4
- Livy, vi.7.1, 8.4-10, 11.9-10, 12.7-11, & 13.1-8
- Livy, vi.6.2-3, 10.6-9, 14.1, 17.7-8
- Cornell, T. J. (1995). The Beginnings of Rome- Italy and Rome from the Bronze Age to the Punic Wars (c. 1000-264 BC). New York: Routledge. p. 322. ISBN 978-0-415-01596-7.
- Oakley, S. P. (1997). A Commentary on Livy Books VI-X, Volume 1 Introduction and Book VI. Oxford: Oxford University Press. p. 356. ISBN 0-19-815277-9.
- Cornell, p. 322
- Oakley, p. 354
- Oakley, pp. 354, 446-114
- Oakley, S. P. (1998). A Commentary on Livy Books VI-X, Volume 2 Books VII-VII. Oxford: Oxford University Press. p. 3. ISBN 978-0-19-815226-2.
- Cornell, p. 324
- Oakley, pp. 3-4
- Livy, vii.1.3-4
- Livy, vii.3.4-9
- Livy, vii.6.1-7
- Oakley, p. 4
- Oakley, p. 72
- Livy, vii.6.11-12
- Livy, vii.7.1-9
- Livy, vii.8.1-7
- Oakley, pp. 4, 103-104
- Livy, vii.9.1
- Livy, vii.11.2
- Livy, vii.11.8-9
- Livy, vii.12.7
- Livy, vii.14.10
- Livy, vii.15.11
- Oakley, p. 4
- Cornell, p. 324
- Cornell, p. 324; Oakley, p. 4
- Oakley, p. 4
- Cornell, p. 324; Oakley, p. 4, 175
- Forsythe, Gary (2005). A Critical History of Early Rome. Berkeley: University of California Press. p. 277. ISBN 0-520-24991-7.