The Congress needs room to operate. If we don't have land on all of the continents, we will not be in touch with problems. Since we are unable to be invaded or invade, we will stay here, without expanding, as we ensure that Waterpatheion does not fall into chaos.
The Congress itself isn't able to invade or be invaded, but its members (Excluding SuchSilliestBilly because it's in his nation's rules that he cannot invade, as long as he cannot be invaded) can invade.