The USA and Britain are involved because they have a treaty obligation to do so.
The former independent Warsaw pact countries are involved because not only do they feel threatened, but they actually have been.
The scandinavian countries are involved because altho they by and large agreed to stay netural while there was peace, Russia couldn't help itself shooting it's mouth off about how hard it is and treatened to take Finland, probably in 3 days.
Turkey just like causing trouble, The dutch want payback for that plane the Russians murdered a load of it's citizens on.
But i get it's complicated and easier to just think............... DUH DUH it's the NATOz fault.