The War Sword requires Exotic Weapon (War Sword) proficiency to use but it is special in that if you have Martial Weapon Proficiency (WarSword) you can use it two handed. Note that many classes are proficient in all martial weapons, but a class that is not does not need to take Martial Weapon Proficiency (War Sword) before Exotic Weapon Proficiency (War Sword) in fact their is no reason to take Martial Weapon Proficiency (War Sword.)
Nordhiemir have Weapon Familiarity: War Sword which means that as long as you have Martial Weapon Proficiency (War Sword) you can use the War Sword in any way you like.
Hyborions have Weapon Familiarity: Greatsword which means that they can weild a Greatsword with out penalty as long as they have Martial Weapon Proficiency (Great Sword)
They have no special advantage weilding the War Sword.
A war sword used two handed can be used as a finese weapon, you don't need anything more than to use the war sword two handed to finesse with it.
Most classes get Martial Weapon Proficiency in all weapons, so most classes can use a war sword two handed with out penalty. But if you were going for a straight thief or scholar and wanted to use a war sword or great sword you'd need to get Exotic Weapon Proficinecy (War Sword) or (Greatsword). Though technically you could get Martial Weapon Proficiency (War Sword) it's be rather pointless except for the fact that you need a BAB of +1 before taking Exotic Weapon Proficiency. A nordhiemir thief though could take War Sword as a martial weapon with out a BAB of +1 and be able to use it one handed because of Weapon Familiarity.
Hope this helps.