Assume a setting where, aside from a few relatively large landmasses (think Ireland), most landmasses are no bigger than 50km in the largest side. These islands drift relatively fast, at rates ranging from a few meters to a few kilometers a day. In this setting, the nations that were founded in these few large islands eventually grow too big and seek to expand.
How would they go about this expansionist drive given there's a very big chance that the lands they conquer will eventually drift far away from them, possibly into the range of rival nations? How would they maintain hegemony over their lands? Would they even try to?
EDIT: Technology-wise, instant communication would be limited to radio, meaning at most a range of 2000km for long wave transmitters.
While the question is aimed at a world of flying islands and no solid surface, I decided to omit this so as to keep it relevant in oceanic worlds and other similar, if more fantastical, alternatives.