Epeiros/History

The history of Epirus was very similar in many aspects to that of Macedonia: located at the northern borders of the Greek world, this region of the Balkans (more or less corresponding to modern Albania) was strongly influenced by both the Illyrians and Greeks.
Being the home of humans ever since the earliest days of man, the hills of Epirus were home to a host of tribes. By the 7th century, however, three tribes eventually became dominant: the Molossians, who claimed descent from the hero Achilles; and the tribal confederacies of the Chaonians and the Thesprotians. Because of the poor soil of the mountainous lands, the Epirotes did not live in citadels or poleis, but instead lived in villages scattered throughout the highlands of the interior. The most notable cities of this land were Ephyra and Dodona — the latter becoming the capital of the Epirote league in the last days of independence in the Classical Era.
===On the Shoulders of Giants===
As with Macedonia, the original semi-barbarous Epirus gradually transformed into a `hellenized’ kingdom, thus becoming one of the most significant Hellenistic states. The three main tribes of Epirus had originally been nomadic groups, constantly at war against the Illyrians from the north. This political situation continued to exist until 370 BC, when the Molossians (the most important of the three Epirote tribes) started to expand at the expense of the other two tribal groups. After some years of internal wars, the Molossians were finally able to unify Epirus and form a centralized kingdom that was ruled by the Molossian royal family of the Aecides. 
After some decades, the new Kingdom of Epirus decided to form an alliance with the Kingdom of Macedonia. The latter was becoming increasingly powerful militarily and the Epirotes needed an ally against the Illyrians. As a result, Neoptolemus I, the first monarch of unified Epirus, married his daughter, Olympia, to Philip of Macedon in 357 BC. When Neoptolemus died, the throne was inherited by his brother, Arybbas, who was later driven into exile by Philip of Macedon and replaced by Neoptolemus’ son, Alexander. The latter was brother of Olympia and thus uncle of Alexander the Great.
===A Taste for Glory: Alexander of Epirus===
Until the ascendancy of Alexander of Epirus, Epirote military forces were simply made of irregular tribal levies, which were very similar to those of the Illyrians. These contingents of light infantrymen, presumably equipped as psiloi skirmishers or traditional peltasts, were transformed into regular troops shortly before the first Epirote expedition to Italy. Alexander of Epirus was a personal friend and loyal ally of Philip of Macedon.
As Alexander had spent most of his early life as a hostage at the Macedonian royal court, it is highly probable that he learned how to reorganize an army from Philip of Macedon and then decided to apply the latter’s military reforms in his country. Epirus was mountainous and inhospitable, with a terrain that was perfect for loose formations of light infantry and not for tightly packed heavy phalangists. In addition, unlike Macedonia or Thessaly, Epirus could field a small cavalry force formed by the few nobles of the country. Under Pyrrhus, however, the Epirote Army soon transformed into a significant military force thanks to the major use of contingents provided by allies or mercenaries.
While his more famous nephew was conquering the Persian Empire, Alexander of Epirus decided to obtain some glory for himself by launching a military campaign in Italy. Epirus was very near to southern Italy and thus became increasingly involved in the local conflicts of the peninsula. In 334 BC, Alexander of Epirus landed in Italy, officially to help the important Greek colony of Taras in its war against the Italic tribes of the Lucanians and Bruttii. The campaign organized to emulate Alexander the Great, however, was a failure and Alexander of Epirus was killed in battle in 331. In the following decades, as we have seen, the Kingdom of Epirus was involved in the Wars of the Diadochi and thus temporarily abandoned any ambition of expansion in Italy, until the reign of Pyrrhus of Epirus.
===Fall of the Kingdom===
After Pyrrhus’ death Epirus reverted to minor power status, first under his descendants and then as a republic, no doubt mostly using citizen troops. However we do have an account of one singularly unfortunate experience with mercenaries. A force of 800 Gauls, allegedly exiled by their own countrymen, had served Carthage in Sicily; they pillaged one city they were garrisoning, tried to betray another, and deserted to Rome. In Roman service they sacked a temple, and so were ejected from Italy as soon as possible. The Epirotes hired this band of desperadoes and set them to garrison the capital Phoinike. True to form, the Gauls betrayed the city to a fleet of passing Illyrian pirates, and the entire population of Phoinike was enslaved! As Polybios says “no people, if wise, should ever admit a garrison stronger than their own forces, especially if composed of barbarians”.
===References===
*Weapons and Warfare, The Epirote Army