Being "military defenseless" is not very important if your claim on the land suddenly recognized by UN states. These states can supply their own manpower.

A Serb or a Russian is just a single ordinary human being. You can oppress them ethnically exactly in the same fashion as you would oppress a small stateless minority.

In short, where you expected to get a bloodless happy independence, you would get a civil war half of the time, and you can blame yourself or your foreign coercers. This is contrary to the rosy picture the USA liked to paint when it plunges countries into civil wars.