First Warlord Eadric Ivanovich is the leader of At All Costs, a secret society within the Order of Rekkenmark that seeks to start and win the Next War by any means necessary. Many of Karrnath's most powerful warlords are members of the society, increasing the taxes they impose so as to fuel their growing forces. Eadric sees a reprisal against the Valenar as the best opportunity to test Karrnath's strength while avoiding restarting the war on the Western half of the continent before he is ready.
While he is somewhat concerned about drawing the bulk of Karrnath's armies away from its heavily settled Western portion, he sees Jaela as too weak to invade and has reliable intelligence about Lord Darro ir'Lain of Aundair's plans to invade the Eldeen Reaches. As such, he feels comfortable extending Karrnath's forces to the south to invade Valenar.
Source: Politics of Karrnath