In the wake of the poisoning, 28 countries expelled suspected Russian spies acting as diplomats. In the early-21st century, especially following the poisoning of Alexander Litvinenko in 2006, relations became strained, and since 2014 have grown unfriendly due to the Ukrainian crisis (2013–) and to activities by Russia such as the suspected 2018 poisoning of Sergei and Yulia Skripal, seen as hostile by the UK and by many in the Western world. Since the 19th century, England has been a popular destination for Russian political exiles, refugees, and wealthy fugitives from the Russian-speaking world. The countries share a history of intense espionage activity against each other, with the Soviet Union succeeding in penetration of top echelons of the British intelligence and security establishment in the 1930s–1950s. Russia's big business tycoons developed strong ties with London financial institutions in the 1990s after the dissolution of the USSR in 1991. The two countries were at sword's point during the Cold War (1947–1989). They allied again in World Wars I and II, although the Russian Revolution of 1917 strained relations. They were enemies in the Crimean War of the 1850s, and rivals in the Great Game for control of central Asia in the latter half of the 19th century. Russia and Britain became allies against Napoleon in the early-19th century. Formal ties between the courts started in 1553. Russia–United Kingdom relations, also Anglo-Russian relations, involve the bilateral relationship between Russia and the United Kingdom. Prime Minister Boris Johnson with Russian President Vladimir Putin at the Libya Conference, January 2020.