[drran]

Why they must declare a war, while Russia and Belarus doesn't? Is there a special international law just for NATO?

[jlokier]

Yes, there actually is international law. It's not just for NATO, it applies to Russia and Belarus as well.

But Russia is ignoring those laws. What Russia is doing is called "war of aggression": https://en.wikipedia.org/wiki/War_of_aggression

"A war of aggression, sometimes also war of conquest, is a military conflict waged without the justification of self-defense, usually for territorial gain and subjugation."