Valtia is a planet inside the defence line, which means it is well secured and the probability of a beast attack is very low. In these kind of planets there is no conscription law, but taxes are higher. People there aren't used with seeing battleships and live a their lives in a peaceful reality, comfortably distant from the hell of the wars. From the events that happened there, it seems that its one of the main planets of mankind.
Valtia is the planet from where Admiral Norton set off to Arin and also where Anne Mayer's retirement party was held. Dry made his speech about proposing the New Alliance and organized it there too.
There's a secret bunker ("Eden") that along with the Zeppelin were supposedly intended to be used for the second "Earth Strike" plan.
Following the Arin attack, the Beasts launched preemptive strikes on several planets, including Valtia (see article for more info). There was some damage, but what really doomed Valtia was Fear's Morglay. The Weapon of Massacre sliced through the outer planet crust and reduced the rotation inertia. Weeks later, the biosphere would have been cursed by a permanent Ice Age.