On action

on_annexation_start

Точный скрипт

effect = {
scope:target = {
add_casus_belli = {
target = root
type = casus_belli:cb_resist_annexation
}
}
every_related_country = {
type = guarantee_vassal_independence
add_casus_belli = {
target = root
type = casus_belli:cb_prevent_annexation
}
}
}