Another angle: could "Czech parties" refer to social clubs or organizations in the Czech Republic? That seems less likely. More plausible is political history. The years 1820 to 2011 would cover the Habsburg Monarchy, Austro-Hungarian Empire, Czechoslovakia, WWII, communist era, Velvet Revolution, and the post-Soviet transition up to 2011. The user might be interested in a comprehensive summary of the political parties during this period, divided into two parts with a focus on two key periods or parties.