Century of Blood
From A Wiki of Ice and Fire
The dominant power in Essos, the Valyrian Freehold, collapsed when the Valyrian peninsula was destroyed through the Doom of Valyria. The colonies and conquests of Valyria broke away and bedlam erupted. The nine Free Cities were formed, only to fall into warfare against one another. On Dragonstone the Targaryens chose not to intervene, hoarding their own strength instead.
Taking advantage of the power vacuum, the Dothraki emerged from the central plains and laid waste to lands surrounding the Dothraki sea. They conquered the kingdoms of Sarnor and Ifequevron and the Ibbenese colony of Ibbish to the north, as well as the Valyrian colony of Essaria to the west. The Dothraki also raided Ghiscari and Qartheen settlements to the south.
Near the end of the century, the Volantenes conquered Lys and Myr. When Volantis attacked Tyrosh, they were repelled by an alliance of Tyrosh, Pentos, the Argilac Durrandon the Storm King, and Aegon Targaryen atop Balerion. The resulting war freed Lys and Myr and laid waste to the Disputed Lands. The militant tiger triarchs of Volantis subsequently lost power to the mercantile elephant party.