Short answers, pulled from the story.
The Sinatra Doctrine was a Soviet foreign policy under Mikhail Gorbachev that allowed Warsaw Pact member states to determine their own domestic affairs without Soviet interference. The name came from a quip by Foreign Ministry spokesman Gennadi Gerasimov, who compared the policy to Frank Sinatra's song "My Way," saying each country could now go its own way.
Gennadi Gerasimov, the Soviet Foreign Ministry spokesman, coined the phrase on the 25th of October 1989 while speaking to reporters in Helsinki. He was commenting on a speech made two days earlier by Foreign Minister Eduard Shevardnadze.
The Brezhnev Doctrine held that Moscow could intervene directly in the internal affairs of Warsaw Pact states to protect communist rule, justifying the crushing of the Hungarian Revolution in 1956 and the Warsaw Pact invasion of Czechoslovakia in 1968. The Sinatra Doctrine reversed that stance, declaring that each country's political structures would be decided by its own people.
By the late 1980s, structural flaws in the Soviet system, growing economic problems, rising anti-communist sentiment, and the toll of the Soviet-Afghan War had made it impractical to maintain tight control over neighboring states. Poland had elected its first non-communist government since the 1940s a month before the doctrine was named, and Hungary had already begun dismantling the Iron Curtain on its border with Austria.
Within a few months of the announcement, communist governments in East Germany, Czechoslovakia, Bulgaria, and Romania had all been overthrown. The doctrine signaled that the Soviet Union would not intervene to defend communist rule, removing the threat that had kept those governments in power.
Honecker condemned the end of traditional socialist unity and appealed to Moscow to rein in Hungary, which was allowing thousands of East Germans to flee to the West across its newly opened border with Austria. The Sinatra Doctrine announcement directly contradicted his appeals, signaling that Soviet support for his government would not be forthcoming.