Former flag of Czechoslovakia and current flag of the Czech Republic.
Upon the dissolution of Czechoslovakia, the Czech Republic kept the Czechoslovak flag while Slovakia adopted its own flag. The first flag of Czechoslovakia was based on the flag of Bohemia and was white over red. This was almost identical to the flag of Poland (only the proportion was different), so a blue triangle was added at the hoist in 1920. The flag was banned by the Nazis in 1939, and a horizontal tricolor of white, red, and blue was enforced. The 1920 flag was restored in 1945.
The traditional colours of the Czech lands, originating from an 1192 coat of arms (depicting a rampant lion with a double silver tail on a field of red).
After the establishment of an independent Czechoslovakia in 1918, the country had been using the red and white flag of Bohemia, identical to the Polish flag. Following calls for a new flag to be adopted by the fledgling state, a committee picked a design by Jaroslav Kursa, an archivist in the Czechoslovak Ministry of the Interior. His design included the red and white horizontal stripes derived from the the coat of arms of Bohemia and added a blue chevron extended halfway
The flag was officially approved by the National Assembly of Czechoslovakia on 30 March 1920 and since then, it has been in continuous use, with the exception of the German occupation of Czechoslovakia during World War II. Additionally, during a short period following the Velvet Revolution, between 1990 and 1992, the Czech part of the Czechoslovak federated state adopted the previous red and white flag.