This answer may not suffice because it hinges upon the last phrase of your question. The papacy has a very poor record in battles and conflicts--nearly every time the papacy has had a military victory it was reversed in the course of the war and it has been extremely rare for the papacy to enforce its will via warfare. As a regional power with a small population it repeatedly fell victim to larger powers. The papacy is also relevant today.

Where this example breaks down is in how we approach your definitions. Does it have to be a country that is still relevant today, or does an entity that once headed a country and now heads a different country meet your criteria? I ask because the Papal States are no more. That country was defeated on the field in 1860-61 for all of its land save Rome, and it lost any military control of Rome in 1870. The Lateran Concordat created a new country: Vatican City. This creation is mentioned in the preamble of the document:

it has been found necessary to create under special conditions the Vatican City

As well as being explicitly stated in Article 3

Italy recognizes the full ownership, exclusive dominion, and sovereign authority and jurisdiction of the Holy See over the Vatican as at present constituted, together with all its appurtenances and endowments, thus creating the Vatican City, for the special purposes and under the conditions hereinafter referred to

So, if you are strict with your definition of "country" and how that relates to "is still relevant today" then the papacy fails your criteria. If one views the papacy or Holy See as the substance behind the Papal States and also as the substance behind Vatican City, then I may have given you an answer that works.