Mont. Code Ann. § 70-28-216

Whenever judgment in an action hereby authorized shall have been entered as to any real property, no other action relative to the same property or any part thereof maintained under this part shall be tried until proof shall first have been made to the court that all persons who appeared in the first action or their successors in interest have been personally served with the papers mentioned in 70-28-209, either within or without this state, more than 1 month before the time to plead expired.