activity_on_war_declared_events_effect

activity_on_war_declared_events_effect = {
	trigger_event = religious_decision.0200 # Stop mediation in its tracks
	if = {
		limit = {
			this.involved_activity ?= {
				is_activity_complete = no
			}
		}
		this.involved_activity ?= {
			save_scope_as = target_activity
			activity_type = { save_scope_as = target_activity_type }
			activity_host = { save_scope_as = target_activity_host }
		}
		if = { # Send one event if you're the host
			limit = {
				exists = this.involved_activity
				this = this.involved_activity.activity_host
			}
			# This event fires follow-up events for the guests depending on the character's choice
			trigger_event = activity_system.0300
		}
		else_if = { # Send another if you're just a guest
			limit = {
				exists = this.involved_activity
				NOT = {
					any_war_enemy = { this = scope:target_activity_host }
				}
			}
			trigger_event = activity_system.0310
		}
		else_if = { # Just go home if you're at war with host
			limit = {
				exists = this.involved_activity
				any_war_enemy = { this = scope:target_activity_host }
			}
			send_interface_toast = {
				type = event_toast_effect_bad
				left_icon = scope:target_activity_host
				title = at_war_difficulty #"At war"
				current_travel_plan ?= { 
					if = {
						limit = { can_cancel = yes }
						cancel_travel_plan = yes
					}
				}
			}
		}
	}
}

As written in game/common/scripted_effects/00_activity_effects.txt.