How did more than 100 foreign diplomats get expelled over one month?

Russia responds to expulsion of its diplomats in more than 20 countries over UK-led ex-spy Skripal poisoning allegations

At least 133 Russian diplomats in 22 countries were ordered to return to Moscow in March, amid a UK-led escalation against Russia over accusations of poisoning former Russian spy Sergei Skripal and his daughter, Yulia, earlier this month.
On 14 March, British Prime Minister Theresa May gave 23 Russian diplomats in the UK a week to leave, identifying them as undeclared intelligence officers. She described the decision as "the single biggest expulsion over 30 years"—estimated at 40% of the Russian embassy's staff—adding, "it is not the first time the Russian state acted against our country."
With more sanctions sought against Russia, the move signalled a severe deterioration of relations between the two countries. The UK further pursued rallying its allies. In the past week, global action against Russia followed.
On Monday, the US announced the expulsion of 60 Russian representatives, with seven days to leave, and ordered that the consulate in Seattle be closed. More than 20 European countries, including France, Germany, and Italy, as well as Canada and Australia also expelled Russian diplomats. Austria abstained from implementing the move.
"Allies expressed deep concern at the first offensive use of a nerve agent on Alliance territory since NATO's foundation. Allies expressed solidarity with the UK, offered their support in the conduct of the ongoing investigation, and called on Russia to address the UK's questions," the NATO said in a statement on 14 March.
NATO Secretary General Jens Stoltenberg said on Tuesday that he has withdrawn "the accreditation of seven staff at the Russian Mission to NATO" and will "also deny the pending accreditation request for three others."
In what international media has called "a tit-for-tat" action, Russia is expected to expel 60 US diplomats, Foreign Minister Sergei Lavrov announced on Friday. The decision is also to include closing down the US Consulate in Saint Petersburg.
Cold War-style, Russia's foreign relations with NATO countries is seriously challenged, and would wait to see whether the UK would be able to mobilise for sanctions on Russia. The Chemical Weapons Convention enforced in 1977 prohibits their use, transfer, and development.
How it all started: Who is Skripal?
Sergei Viktorovich Skripal is a former Russian military intelligence officer. In the 1990s, Skripal served in the Main Intelligence Directorate (GRU). Reports say he was recruited by the British intelligence service (MI6) for which he began working in 1995 and provided with classified information on the Russian state, including exposing a number of undercover agents.
Skripal was arrested in 2004, convicted by Russia in 2006, and was sentenced to 13 years in prison for treason. Authorities said he began spying while stationed overseas and continued after he retired from the Russian military in 1999.
Skripal was freed in 2010 as part of a spy swap agreement with the United States. His release was pushed for by the UK as he later moved to Salisbury.
On 4 March, Skripal and his daughter Yulia were found unconscious on a public bench and taken to hospital. Yulia is reported to be in better condition while her father remains in critical condition.
Investigators believe the pair was poisoned by nerve agents on the front door of his house in Salisbury. Yulia had arrived from Russia to visit her father. The nerve agent used is believed to be of the Novichok group.
Why did the UK accuse Russia?
The Novichok nerve agent was developed by the Soviet Union between 1971 and 1993. Novichok causes the heart to slow and the airways to restrict, leading to death by asphyxiation. Nerve agents are typically inhaled or absorbed through the skin.
It was identified by May as the nerve agent used against the Skripals, thus arguing that it was highly likely Russia was behind the attack.
"We actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purpose of assassination, but has also been creating and stockpiling Novichok," British Foreign Secretary Boris Johnson said in an interview on BBC.
The case has similarities to the killing of former Russian spy Alexander Litvinenko, who was poisoned with radioactive tea in London in 2006.
Patricia Lewis, research director for international security at Chatham House, said Novichok agents could be identified because they have distinct chemical formulae. "There could be contaminants that would give away where it has come from," she told The Independent, adding that high-resolution trace analysis could detect pollen and other clues.
The EU said it took the British accusations seriously, refraining from reaching an immediate conclusion and demanding that Russia comply with questions and demand to provide full disclosure of its Novichok programme to the OPCW.
Russia reaction
Moscow has handed notes of protest to the ambassadors and announced the expulsions of the same number of diplomats—on average, between one to four diplomats. They were given several days to leave the country, Russia Today reported on Friday.
Moscow denied the accusations and criticised the UK for the claims and demanded investigations to be conducted by the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Hague.
In a heated debate at the UN Security Council over the matter, Russian representative Vissaly Nebenzia even suggested the UK might have plotted the attack on Skripal to tarnish Russia, especially ahead of the 2018 World Cup. More importantly, he denied that his country had ever made or even researched the Novichok nerve agent.
Foreign Ministry spokesperson Maria Zakharova said, "Russia has repeatedly addressed the British authorities through official channels with a proposal to establish cooperation in investigating the alleged poisoning of Russian citizens, as well as with requests to provide information on their condition and, of course, the circumstances of the incident" but received no response.
She also said they were denied contact with the Skripals despite them being Russian citizens. "We were forced to learn from the media the date and the time of the incident, the number of people involved in it, and the level of damage to their health," she added.
Moscow is hosting the 2018 FIFA World Cup, condemning Johnson's suggestion that the upcoming competition is comparable to the 1936 Olympic Games under Hitler.
"Mr Johnson," said Zakharova, "Do you not find it shameful and, as you like to say, ‘emetic' that so many British officials attended the opening ceremony of the 1936 Olympic Games? What were all those respectable British sporting functionaries and lords doing as Hitler's guests? Tell your countrymen about this."
A Tuesday report by the Washington Post highlighted reactions by Russian diplomats on Twitter saying the country is "very good at appearing unfazed" and "trolling."
The Russian involvement in the matter is dismissed by some who do not believe the government would seek to murder Skripal after allowing his release, and that the Kremlin would avoid carrying out such an assassination ahead of a presidential election and other areas of tensions over Russia's involvement in the wars in Syria and Ukraine as well as allegations of its interference with the 2016 US elections.