The Holocaust

No written order from Hitler authorising mass murder has ever been found, which means historians reconstructing exactly when the decision to exterminate Europe's Jews was made are working from bureaucratic traces rather than a single smoking gun.

Historians still argue over exactly when Hitler decided to murder every Jew in Europe, a question the record calls unresolved even though it agrees an explicit order existed by the war's later years.

Hitler wanted Czechoslovakia's factories more than its territory, and the occupation's relative restraint compared to Poland reflected that economic calculation as much as any racial theory.

1863

Historians cannot even agree when World War II began, with credible starting dates ranging from 1931 in Manchuria to 1939 in Poland, a six-year spread for the deadliest conflict in history.