* @param slot The slot within <code>Europe</code> to select the unit from.
     * @param type The type of migration occurring.
     * @return An <code>Element</code> encapsulating this action.
     */
    public Element emigrate(ServerPlayer serverPlayer, int slot,
                            MigrationType type) {
        ChangeSet cs = new ChangeSet();
        serverPlayer.csEmigrate(slot, type, random, cs);

        // Do not update others, emigration is private.
        return cs.build(serverPlayer);
    }