Some time after the Second War, Gilneas left the Alliance. During the Cataclysm, Forsaken forces invaded Gilneas. The night elves came to the aid of the Gilneans, but the city still fell. The Gilneans, many of them now worgen, retreated to Darnassus and re-joined the Alliance. Genn was mad at the Forsaken for destroying his city, and developed a strong hatred against Sylvanas Windrunner for killing his son, Prince Liam Greymane.
During the Burning Legion's third invasion of Azeroth, High King Varian Wrynn was killed on the Broken Shore. Varian's son Anduin became the High King of the Alliance, and Genn assumed control of Alliance military forces in the Broken Isles. Genn led the Skyfire into battle against Sylvanas and a Forsaken fleet in Stormheim.