Convention is Ukraine, no “the” before it.
I do not know the reason for sure.
However, if I had to guess, it is because that is how Ukrainians and Russians would do it. They don’t use articles as in English in their language. If you ever edit anything written by a less than fully English literate person from there, expect to add and fix articles.
I simply made that error because I was in a hurry.
Just guessing, I kinda thought it might have originally come from American military references and usage in WWII and after, maybe, but I never really knew. Same reasoning for how the names of some cities there are spelled, also.
Anyhoo, no judgments and please forgive me if I sounded critical instead of just being curious and having an opportunity to ask someone about it.
Cheers!