The War of the New Princes refers to the Essosi conflict in which Khal Joro, following the command of the Braavosi Sealord Myrios Nestoros, sacked several Free Cities before being defeated at Myr, Myrios himself later falling to the armies of Lys and Dorne. The war took place between 501AC and 503 AC.
Myrios Nesteros, the Sealord of Braavos, was a rumored opium addict. He contracted with a Dothraki horselord named Kahl Joro and began sacking Free Cities sometime around 501AC.
After successfully sacking Pentos, Norvos, and Volantis, the horselord was stopped at Myr. The city's magisters had lured the Dothraki to their seemingly lightly defended walls only to envelop the army from behind.
Kahl Joro himself led a small army to one of the magister's palaces, where he faced Ser Ulrich Dayne in one to one combat and forfeited after the knight cut his braid. With his army scattered, he returned to the Great Grass Sea in shame.
Myrios continued forcing his influence on the other cities, reforming Braavos' satellites into a Braavosi Empire, bringing in many laws that proved highly divisive in his home city, such as legalising slavery. His influence in Lys would lead to backlash in the Anti-Braavosi Riots due to manipulation from Lyaan Ormollen.
The Sealord, whilst recovering his strength in Volantis, sent soldiers to "protect Braavosi property and interests." Although they never arrived, the newly crowned Prince of Lys, Varyo Velaryon, called upon his alliance with Dorne and the Martell Princess. She sent her armies under the command of her husband, Prince Martyn Dayne, to join with Lys and they defeated Braavos.
The Sealord himself was never found, presumed to have shipwrecked and drowned in one of the many violent storms that occurred during the Spring Without Sun, and a new Sealord was elected in the ashes of the city.
The Sack of Pentos
Pentos was the first city to fall to the Dothraki. It was burned and left in ruin, and forced to appeal to the Iron Bank of Braavos in order to rebuild, as the Sealord had planned.
The Sack of Norvos
Norvos followed soon afterwards. The city was sacked and looted and again the Iron Bank was brought in to finance the reconstruction. Many of the Free City rulers began to suspect Braavosi involvement.
The Sack of Volantis
The Sack of Myr
The Kahl attempted to sack Myr but his army was taken from behind at unawares. Joro himself was defeated in single combat by Ulrich Dayne. As a result, many of the war's refugees saw him as a hero and flocked to Dorne for safety.
Victory on the Plains
Prince Varyo and Prince Martyn defeated the sellsword armies of Braavos on the Orange Coast. One of the Sealord's armies turned their cloaks, and in exchange Prince Varyo allowed them to loot the city.
Volantis was left in the control of a Sellsword Council with prominent families. The weakness of the city would later cause unrest with the northern cities under their control.
Lys' power was solidified by their victory in the war, the city becoming the prime power amongst the Free Cities. Varyo Velaryon attempted to form a 'Concert of the Daughters' to oversee a continued peace, refusing offers from Syrio of Myr and Tyrosh to attempt another reforming of the Freehold.
With the disapearence of the Sealord, Terro Tregar came to power in Braavos.
"Vranhar still gave him sleepless nights, even after all those years. Luconis wondered what the youth made of Myrios’ War - did he regret not wetting his own blade, proving himself in the fires of combat? Did he thank the gods he had not fought on the beaches for the Sealord’s folly, or did he despise those who did for their failure? Whatever his generation thought was a mystery to Luconis, and an irrelevance, for they had not been there." - Luconis Antaryon