It does? You think they expanded into the Taus and took over Leeds for such a petty reason? Please.
Gallia doesn't have a problem with Kusari or Rheinland. Actually if anything, they find them to be great trade allies. Gallia only went to war with Bretonia and Liberty decided to join in because of the bret-lib alliance. It's not Gallia vs Sirius.
edit: @Thunderer Yeah, lore made by Igiss. A lot of lore has changed since Igiss was around, including the strengh of the navy. It's more around 250-300 at the start if anything.