When Poland was attacked in 1939 by Germany, he wrote an important poem encouraging Poles to put away political differences and fight the aggressors. After Poland was invaded by the Soviet Union, Broniewski found himself in Soviet-occupied Lwów. His poems were printed in a Soviet-published newspaper, but he was soon arrested by the NKVD on trumped-up charges of "hooliganism". He refused to co-operate with the NKVD and after four months was transported to the Lubianka prison in Moscow, where he stayed for thirteen months. Afterwards, he worked at the Polish embassy in Kuybyshev. He left the Soviet Union with the Polish army led by General Władysław Anders and through Iran came to Iraq and then Palestine.