From A Wiki of Ice and Fire
The Disputed Lands is an region on the continent of Essos. It has been contested between the Free Cities of Myr, Tyrosh and Lys since the fall of Valyria, over three centuries past, usually involving skirmishes and small wars. Mercenaries are usually hired to fight the battles, and several nobles from Westeros, such as Ser Jorah Mormont and Prince Oberyn Martell with the Second Sons, have fought in the wars.
Numerous wars have been fought over the Disputed Lands. Among the more notable to Westerosi include the war that created the Kingdom of the Three Daughters that unified the region for over thirty years, and when the Band of Nine conquered the Disputed Lands as first step in their campaign leading to the War of the Ninepenny Kings. The Lands were eventually lost once the Nine's efforts began to fail.
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