AI does not attack (Crusader Kings 2)

I play for about 500 hours (and for Ireland, England, India, Stepnikov, Slovyan), and I have NEVER been attacked by another state. For example, in part 3, as soon as someone has a claim to my title, and this ruler is stronger, he declares war on you, but in part 2, for some reason, nothing. Only adventurers and prepared invasions (eg Vikings) attack. Maybe it's a bug or not?