The moment is etched in the lore of Vladimir Putin: The Berlin Wall had just succumbed to hammers, chisels and history, and a KGB officer still shy of 40 and stationed in Dresden, East Germany, was in a panic, burning documents and requesting military support as a crowd approached. “We cannot do anything without orders from Moscow,” Putin was told on the phone. “And Moscow is silent.” In an interview appearing in his 2000 book, “First Person,” Putin recalls that dreadful silence. “I got the feeling then that the country no longer existed,” he said. “That it had disappeared.” Two years after the wall went down, the Union of Soviet Socialist Republics did, too. A decade after, Putin would ascend to power in Russia, talking about a revival.