Martina Navratilova has voiced her commitment to fight for democracy and hope on the 55th anniversary of the Warsaw Pact invasion of Czechoslovakia.

On August 20-21 1968, Czechoslovakia (now the two separate countries of Czechia and Slovakia) was invaded by four nations belonging to the Warsaw Pact, a collective defense treaty established by the Soviet Union.

The invasion brought an end to Alexander Dubcek's Prague Spring liberalization reforms, which were an attempt to bring greater freedoms of speech, press, and travel to the Eastern bloc country as an act of partial democratization. Instead, the invasion strengthened the authoritarian wing of the Communist Party of Czechoslovakia to ensure greater restrictions were re-imposed.

The 18-time Grand Slam champion took to Twitter to remember the invasion. Navratilova was born in Prague, Czechoslovakia in 1956, meaning she was just a child when the invasion happened.

"Today , August 21st 1968, 55 years ago, the Warsaw pact army, at the behest of Soviet Union, invaded then Czechoslovakia. I will never forget that day when hope was crushed. Which is why I will keep fighting for fairness and democracy and hope wherever I happen to be…." she wrote.

Navratilova lived in Czechoslovakia until the age of 18 and struggled with the travel restrictions that stopped her from participating in tennis tournaments in the United States. Therefore, she took the huge decision to seek political asylum in the latter country.

In order to secure asylum, Navratilova had to pause her tennis career and spend a significant amount of her earnings. She also lost her Czechoslovakian citizenship, but was granted American citizenship in 1981.

The now 66-year-old then went on to win a combined 59 major titles across singles, doubles, and mixed doubles, the most in the Open Era, and she is widely considered to be one of the greatest tennis players of all time.