Threat of Attack

[Maltz]

Curious about the "Threat of Attack" message (screenshot now included) we receive at the beginning of a turn. From my limited experience:

(1) The subject of the threat ALWAYS declares war on the next turn. I have read people successfully delay this attack by drastically improving the relationship with the subject, though.
(2) My border province with the subject of the threat is undefended at the time, although I could reinforce it in a turn.
(3) The subject's invasion army is within my clan's view (by trade route, ninja, etc.)
(4) I only receive "threat of attack" at most once per campaign. Sometimes not at all.

What's your experience with threat of attack?