this also relates to the way that modern governments define their hegemony as "including" ... list of things that is the waterways and coastline areas. NOT the land, because it's based on maritime law. they are not allowed to claim the land.
it's also quite relevant with the impending geomagnetic pole shift/micronova event coming that the largest region, with likely good weather during a minor glacial period, that is almost certainly following the disaster, cuts a line straight through about the balkans and the eastern edge of africa (of which, there is a very big rift that is about to open up in northeast africa as well, could become new land and/or an island forms). the right places to be on the planet now are basically, the region around the carpathians, the mongolian plateau, the eastern rocky mountains. almost everywhere else is going to be washed away into the ocean bed.
obviously, this is a major advantage for the eurasia region, since essentially it's likely to have the greatest internal navigability as well, as almost certainly there will be new seas forming and potentially straights, like, the region around southwest siberia is likely to sink and baikal turn into a sea.
anyhow, yeah, if eurasia gets its shit together, it can become a lot harder to control. all the resources are available to one single land connected region, and it would presumably be connected by railways. it's also notable that railways have been quietly sabotaged and removed from the transport equation in most of the western world. one of the few places i know of in the world where rail is still a primary transport is Bulgaria. even next door serbia has muntered most of their main long haul rail network, yes, in favour of highways. the highways also, seem to be something the thallassocrats focus on. i hate roads, rubber wheels and trucks and highways. horrible things, noisy, dirty, disgusting. and dangerous.