He chose to build a wall, that caused a civil war, then he chose to abandon the people of Lordaeron, despite their pleas for help, then he ordered the worgen released, who spread and ruined his nation forcing the population into hiding and then while hiding in a corner of his ravaged and sacked kingdom the forsaken started their invasion, sone of them sill holding a grudge, because the gilneans left them in their most dire hour. So by the time the forsaken arrive Gilneas had pretty much ceased to exist