Things we believed during the Cold War that ended up being wrong

The USSR could have survived indefinitely
The total collapse of the Soviet Union at the beginning of the '90s caught everyone off guard. It had been clear since 1985 that things were changing, what with Gorbachev's reforms and Rocky KO-ing Ivan Drago, but no one expected the planet's second superpower to go completely kaput. The thinking was that the USSR was here to stay. Relations might get better or they might get worse, but the only way the Soviet empire was vanishing was in a cloud of radioactive dust.