

The Polish government-in-exile, was the exiled government of Poland that existed from the German invasion of Poland in 1939 (hence the exile) to the return in 1990.
In September 1939, Germany, Slovakia, and the USSR invaded Poland and the government went into exile in allied countries.
Some Polish forces survived the invasion and fled to the allied countries and would fight in the Fall of France, in 1941, POW’s captured by the Soviets, were freed due to the axis invasion of the USSR (operation Barbarossa) and would fight with the British in the invasion of Iran, Italian campaign (Participating in the Battle of Monte Cassino and liberating Bologna), and the western front (helping to liberate France).

In the occupied areas, resistance rose up fighting the Germans. They also caused uprisings like the Warsaw uprising (Most of them crushed).
The Yalta conference agreed that the western allies would not recognise the government-in-exile, instead, they would recognise the communist provisional government of the Republic of Poland.
the resistance would continue to fight the communist regime but would end in 1963.
The government would return to Poland in 1990 when the Communist Bloc was ending.
Władyslaw Raczkiewicz (as President from 1939–1947)