In March 1939 Czechoslovakia was overrun by the Nazi German forces and immediately underground resistance was started. An emergency government was set up in exile in London and shortly after the outbreak of WW2 in September, military units were formed, first in France and later in Britain. These units were made up from Czechs living abroad at the time as well as from a number that managed to escape from their occupied homeland. On the other hand, a Slovak puppet state, controlled by the Germans, was set up under Mgr. Josef Tiso in March 1939 and cooperated fully with the occupying forces.