Unofficial figures are much larger. It is estimated that between 1948 and 1989 close to 1 million people left communist-ruled Czechoslovakia. The largest exoduses occurred following the communist takeover in February 1948 and following the Warsaw Pact invasion of Czechoslovakia in 1968, with around 200,000 people leaving in each wave. A very similar 200,000-strong refugee wave left Hungary in 1956 after their failed anti-communist revolution. In the 1950s, when the regime was at its harshest and the "Iron Curtain" was close to impenetrable, emigration was very low. It increased between 1969 and 1989, when close to 40,000 people were leaving the country each year. All of them were sentenced to imprisonment "in absentia" by the communist regime for leaving the country illegally.