What’s a historical fact that would shock most people to find out?

"During the Second World War, around 11 million Slavs have been systematically murdered by Nazi forces in a war of extermination in Eastern Europe. Part of Generalplan Ost, the extermination was aimed not just at forcing Slavs into slave labour, but at physically exterminating big parts of the Slavic people. These murders were planned by the Nazi leaders. Although the Second World War and its horrors are a big part of our contemporary society, the genocide on the Slavs has been kept remarkably silent." -- THE FORGOTTEN HOLOCAUST Lennart Lens, Leiden University