Following the liberation of Cyrenaica, the Nesiotic League was finally seen by the Seleucids as a viable threat to their status in Asia Minor. They quickly annexed Atropatene and large swaths of Armenia, and vassalizing the latter's king in exchange for keeping what little lands they had left.
Pontus had always feared the League's might since the loss of Bithynia, and they too sought to increase their power by annexing Cappadocia, with the Seleucid Empire's blessing.
In 523, Sthenelaus Omirid was elected Archon, but his term in office was consumed by the civil strife his election prompted. His fierce rival Teleclus Xenonid, who had expected to be elected, revolted after the election results were announced. Thus began the First Nesiotic Civil War. If it could be called a war. Teleclus drew the sympathy of many, but not of any soldiers. His small militia inevitably fell before the might the League's loyal armies. After a year and half of fighting, the dissidents were finally annihilated and two months later, the legendary general Lysimachus died at the age of only 40... reminiscent of Alexander, it would seem the greatest of Greek generals die young...
While the Omirid family had always been a political powerhouse since the beginning, (Ikesios Omirid the Elder was the League's first general and second Archon), with the victory in the civil war, and the death of the popular Lysimachus and other potential political opponents, Sthenelaus began what is known as the "Omirid Dynasty" in Nesiotic League history.
In 525 Phocas Omirid was elected and his rule was remembered mostly for building many new irrigations and forums in the northern colonies and the liberated Greek lands of Asia. But also during his term, the Romans approached their fellow Republic with an offer of alliance in case of Seleucid, Carthaginian or Dardanian aggression. Omirid agreed, forming the most powerful alliance the world had yet known, and that no power in the Mediterranean would dare challenge.
In 527 another Omirid, Damasias, was elected Archon, and during his term rebels in the Bosporan Kingdom overthrew their government and refused to continue paying the League's tribute. Damasias quickly organized an invasion of the small Greek kingdom.
The ragtag revolutionaries killed more soldiers than they lost, but they simply could not hold back the superior numbers of the League. Menon Omirid captured Panticapaeum after a year-long siege while Ikesios Omirid (the Younger) marched from Rhoxolani lands straight to the capital at Phanagoria, defeating the Bosporan army along the way. After one year of fighting, the Bosporans ceded Panticapaeum and Maoetae, but refused to pay tribute.
A year later, Olbia, facing mounting debt due to their tributary payments, could no longer afford them and they were quickly annexed.
In 531, Menon Omirid was elected Archon, at a time when tensions were once again beginning to mount with Pontus and the Seleucid Empire.... would the alliance with Rome hold?
The Nesiotic League in 531 AVC
Comparison of major powers, sorted by research