Beria was the longest-lived and most influential of Stalin's secret police chiefs, wielding his most substantial influence during and after World War II. Following the Soviet invasion of Poland in 1939, he was responsible for organizing purges such as the Katyn massacre of 22,000 Polish officers and officials. Beria would later also orchestrate the forced upheaval of minorities from the Caucasus as head of NKVD, an act that was declared as genocidal by various scholars and in 2004 as concerning Chechens by the European parliament. He simultaneously administered vast sections of the Soviet state, and acted as the "de facto" Marshal of the Soviet Union in command of NKVD field units responsible for barrier troops and Soviet partisan intelligence and sabotage operations on the Eastern Front during World War II. Beria administered the vast expansion of the Gulag labour camps, and was primarily responsible for overseeing the secret detention facilities for scientists and engineers known as .