According to Wikipedia the Ukraine has signed onto all the Geneva Conventions and all the Protocols.
I can imagine a little guy from the UN in green eye-shades arriving in Kiev just after Independence asking them to “sign here” to gain international recognition.
Seriously, I don’t know how that works. Perhaps you inherit certain treaty obligations? I would think that you’d still have to affirm them.
That would make sense, either inheriting those treaty obligations or being pressured into making them anew.