croatia was already funny shaped when it was in personal union with the kingdom of hungary. that's the upper half of modern croatia. most of the lower thin bit was dalmatia, which was also historically inhabited by croats and unified with (a newly independent) croatia immediately after ww1.

so while yeah, it looks like the west meddled to deny serbia access to the sea, i dunno how true that is. the region really was mostly croats and some italians, i think...

i could much more easily believe that montenegro was the result of such meddling