Sack of Lannisport

"During the Dance of Dragons, the Red Kraken picked the side that was fighting the Lannisters and fell upon the Westerlands while the Lannisters were off at war. Casterly Rock itself proved too strong once the lady of the castle barred its gates, but the ironborn burned the Lannister fleet and sacked Lannisport carrying off gold, grain and hundreds of women and girls including Lord Lannister's favorite mistress and all his bastards."

- Euron Greyjoy The Sack of Lannisport was part of a campaign of the House Greyjoy against the Westerlands during the Dance of the Dragons. Although Dalton Greyjoy, the Red Kraken had passed his offensive as an action in favor of Rhaenyra Targaryen, this was in fact an excuse for the Ironborns to resume their Old Ways of raiding and enslavement on the coast of the  Sunset Sea. The success of the Greyjoy offensive led them to maintain their attacks on Westeros until after the end of the Targaryen civil war.

It is only mentioned in Histories & Lore.

Dalton Greyjoy in the Dance of Dragons
The Dance of the Dragons began after the death of King Viserys I Targaryen in 129 AC when Dalton was sixteen. The Red Kraken is said to have laughed after hearing of the outbreak of war.

The greens of Aegon II Targaryen offered Dalton the position of master of ships and the admiralty to replace Ser Tyland Lannister, who had been made master of coin, if Dalton would bring his ships around Westeros to battle Lord Corlys Velaryon, the Sea Snake. Instead of leaping to the offer, Dalton waited to see what the blacks had to offer.On the black council, Prince Daemon Targaryen suggested appealing to Dalton's bloodlust to bring him on the side of Rhaenyra Targaryen. Instead of asking him to sail to Blackwater Bay, Rhaenyra only asked for Dalton to attack her enemies.

The Red Kraken chose black over green, deciding to attack the nearby westerlands, vulnerable with Lord Jason Lannister campaigning in the riverlands. His wife, Lady Johanna, barred the gates of Casterly Rock but was unable to protect the rest of the west. Dalton burned the fleet of House Lannister and sacked Lannisport, carrying off gold, grain, and trade goods. Hundreds of women and girls were taken as salt wives, including the favorite mistress of Jason and their natural daughters. Dalton led the capture of Kayce, and after the fall of Fair Isle Dalton claimed four of Lord Farman's daughters as salt wives, giving the fifth, the "homely one", to his brother Veron. Lord Jason was killed in the Battle of the Red Fork in 130 AC.

For the better part of two years, the Red Kraken ruled the Sunset Sea like the driftwood kings of antiquity. The regency of Aegon III commanded Dalton to cease his raiding, but the Red Kraken ignored them.