Wars have started over lesser offenses...
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The Mongols sacked Baghdad and brought down the ‘Golden Age of Islam’ to dust and rubble, when the Muslim ruler there assaulted and executed a Mongol messenger.
The sultan was trampled to death under carpets in his palace by Mongol horsemen.
She does have the diplomatic immunity:
While the deputy consul’s lawyer has argued that she should have diplomatic immunity, US officials said that would only cover crimes committed in connection with her work.
However the "US Officials" - who, obviously, are A-OK with starting the World War III by arresting a diplomat from a friendly (until now) nuclear power - are creatively reinterpreting the international law. Everyone knows that diplomats are immune from *all* allegations of the host state:
Diplomatic immunity is a form of legal immunity and a policy held between governments that ensures that diplomats are given safe passage and are considered not susceptible to lawsuit or prosecution under the host country's laws, although they can still be extradited.
It is customary that the offending diplomat is tried at home, and punished if convicted. However the host state can only order them to leave, and they must obey.
In this case the diplomat was arrested on allegations of hiring someone who should not have been given a visa, and not paying her the minimum hourly wages. Those allegations, in civilized countries, are investigated by the detective who simply sends the suspect a subpoena to show up at the police HQ and explain herself. No arrest is needed. Whatever transpired was done intentionally, to harm the USA - and it did that harm, just as planned.