can_potentially_call_ally_trigger

can_potentially_call_ally_trigger = {
	# Can never call vassals to your own wars (their obligations are met via taxes and levies!)
	custom_description = {
		text = cannot_call_vassal_to_war
		$JOINER$ = {
			trigger_if = {
				limit = {
					NOT = {
						# Diarchs can join against other vassals.
						this ?= $WARRIOR$.diarch
						# Confederation members can join the confederation leader's defensive wars
						AND = {
							is_confederation_member = yes
							$WARRIOR$ = {
								is_member_of_confederation = $JOINER$.confederation
							}
						}
					}

				}
				NOT = {
					target_is_liege_or_above = $WARRIOR$
				}
			}
		}
	}

	# Can never call your liege to your own wars (they protect you only from foreign invaders, by being the war target instead of you) -- Unless you have the Nomadic Contract Right
	custom_description = {
		text = cannot_call_liege_to_war
		$JOINER$ = {
			trigger_if = {
				limit = {
					target_is_vassal_or_below = $WARRIOR$
					$WARRIOR$ = {
						vassal_contract_has_flag = vassal_contract_liege_forced_war_override
					}
				}
				always = yes
			}
			trigger_else_if = {
				limit = {
					$JOINER$ = {
						NOT = {
							target_is_vassal_or_below = $WARRIOR$
						}
					}
				}
				always = yes
			}
			trigger_else = {
				always = no
			}
		}
	}
}

As written in game/common/scripted_triggers/00_war_and_peace_triggers.txt.