By Ben Aris in Berlin After a four-month offensive, Russian troops captured the fortress town of Avdiivka on February 19. The settlement had formed a key bulwark of Ukraine’s defence line in the Donbas for nearly a decade, having been the scene of heavy fighting in the initial conflict in 2014-15. Is Kupiansk their next target? The fall of Avdiivka has been a real blow to the Western allies and its hopes for a Ukrainian victory, as it hands the initiative to the Russian forces. The mood was made worse by opposition figure Alexei Navalny’s death on February 16 that has crush the dream that Russ…