Do countries at war always treat each other's diplomats as personae non gratae?

Question

On December 7, 1941, Japan launched surprise attacks against the U.S. naval bases at Pearl Harbor, Wake Island, and the Philippines, and on that same day Japan's diplomats in Washington were declared personae non gratae.

I have long more-or-less unthinkingly assumed such expulsion of diplomats just after the commencement of a war is how it's always done, if there are diplomats to expel. But now I remember that in 1782, when Britain and France were at war against each other, France admitted British diplomats whose purpose was to negotiate with American diplomats in Paris. The U.S.A. was then allied with France. In November 1782, when the British and American negotiators agreed on the content of a peace treaty, they called the document the "preliminary articles of peace" rather than calling it a proposed peace treaty to be submitted to higher authorities in both countries for approval. (Maybe I'm mistaken, but I think) that was because a treaty between the U.S.A. and France signed in 1778 said that neither would conclude a separate peace with Britain, and France was still at war with Britain.

One can imagine a diplomat from an enemy country being admitted in order to discuss whether peace can be concluded if a certain agreement on an international boundary can be reached or to discuss details of an exchange of prisoners of war, or perhaps for some other purposes.

What are current usages concerning admission of diplomats from enemy countries?

Answer 1

The outbreak of war is by definition the end of diplomatic relations. By international convention, diplomats are expelled from the host nation (in the rare cases where they haven't been pulled by their own nations), not imprisoned as enemy combatants. The nations involved can still negotiate a diplomatic presence for limited and particular purposes, essentially the age-old practice of sending someone to parlay with an enemy. However, they don't allow a permanent diplomatic presence because that would have no positive purpose and would create a potential hub for espionage.

Answer 2

The functions of a diplomatic mission consist, inter alia, in representing the sending State in the receiving State; protecting in the receiving State the interests of the sending State and of its nationals, within the limits permitted by international law; negotiating with the Government of the receiving State; ascertaining by all lawful means conditions and developments in the receiving State, and reporting thereon to the Government of the sending State; promoting friendly relations between the sending State and the receiving State, and developing their economic, cultural and scientific relations https://en.wikipedia.org/wiki/Diplomatic_mission#Role

Pretty few if any of those roles would still be welcomed between countries at war. They could still be in contact with each other, but diplomatic relations and diplomatic missions usually mean to imply a closer cooperative relation than just continue talking. Also those talks might not even be done by diplomats of the respective country directly but either by neutral states or take place in neutral states.

The thing is there are various practical problems with the diplomats remaining in that country. On the one hand they are basically perfect spies (some probably already are), but in general they are granted immunity from crime cannot be molested, imprisoned or otherwise be mistreated just send home and they are free to regularly and secretly talk to their sending country and exchange information uninhibited and without surveillance. So they have at the very least access to the cultural climate, the public announcements, the propaganda narratives and where any information could be of value that can be dangerous for the host country, while on the other hand they might have authority to negotiate on behalf of the sending country yet are in another hostile country, where they could be coerced and where their vulnerable position could be exploited. That would be highly illegal, but to monitor that would be difficult.

So according to this answer from the history stack the usual course of action is to lock down the embassy hand it over to neutral country and allow the diplomats to leave the country via a neutral 3rd party.

The thing is even in war when you might say "what are they going to do, go to war over it?", diplomats are still expected to be treated correctly because the international community protects their rights due to their vulnerable position which includes that of their own diplomatic missions. So mistreating diplomats could be seen as an act of war not just against that country but against the internal community and might get much more countries involved.

Also yeah personae non gratae is the plural of persona non grata.

Answer 3

On December 7, 1941, Japan launched surprise attacks against the U.S. naval bases at Pearl Harbor, Wake Island, and the Philippines, and on that same day Japan's diplomats in Washington were declared personae non gratae.

There's some backstory that helps answer the question in general. The Japanese Ambassador at the time was Kichisaburō Nomura

The retired Admiral, and in fact the entire Japanese Foreign Office, was kept in the dark as to the Japanese Navy's impending attack upon Pearl Harbor. Nomura and Kurusu had to decode the radioed message of Japan's breaking off of the negotiations with the United States, which practically meant war. It was sent from Japan on Monday, December 8, Japan time, and received while the Washington embassy's technical support staff were still on their Sunday off. Nomura stated that was why he was unable to deliver the message until after the actual attack had taken place.

Normally, when war breaks out, ambassadors and their entourage are expelled from the country. In the case of Nomura, he was sent a message basically declaring war, and had the ignominy of taking too long to decode it. He delivered it long after the attack on Pearl Harbor had started.

Both he and the US ambassador were held until there could be an exchange, which did not happen until later in the war. Neither were mistreated, just under a sort of house arrest.

What are current usages concerning admission of diplomats from enemy countries?

While Russia isn't at war with everyone, the Ukrainian War has prompted many countries to expel Russian diplomats, most of whom are NATO members

The Russian invasion of Ukraine in 2022 resulted in an unprecedented reaction in diplomatic circles against Russian diplomats; over 200 were expelled by 5 April 2022, just days after the disclosure of the killing of civilians in the Bucha massacre. The declared intention was to limit Russia's ability to destabilize the EU and NATO countries.

Answer 4

The normal way is that the diplomats go away on the spot, at most in one or two days. They might remain longer only in an extraordinary reason, for example if the country does not consider the war declaration really serious.

Reason is very simple, you are there to talk with them, but they are coming to kill you.