It's not a declared invasion. I've read headlines that said Russia had "declared war"; in the body of the article, it turns out that Russia has sent a "peacekeeping force" into Donbas. There's been no declaration of war. Russia has responded to requests for help from the rebel leaders in Donetsk and Luhansk.

I mean, there is a war; Russia has been bombing and rocketing Ukrainian military installations all over the country. But it's not a declared war.