Camps for Russian prisoners and internees in Poland that existed during 1919-1924 housed two main categories of detainees:

• personnel of the Imperial Russian Army, and Russian civilians, captured by Germany
  Germany
  Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
  
   during World War I
  World War I
  World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
  
   and left on Polish territory after the end of the war; and
• Soviet military personnel captured during the Polish-Soviet War
  Polish-Soviet War
  The Polish–Soviet War was an armed conflict between Soviet Russia and Soviet Ukraine and the Second Polish Republic and the Ukrainian People's Republic—four states in post–World War I Europe...
  
  , the vast majority of them captured as a result of the battles of 1920.

Due to epidemics raging at the time, made worse by the very bad sanitary conditions in which the prisoners were held, largely due to overcrowding, between 16,000 to 20,000 Soviet soldiers held in the Polish POW camps died, out of the total of 80,000 to 85,000 prisoners.

Some politicians and historians in Russia have tried to use these deaths to explain the motives for the Katyn massacre

Katyn massacre

The Katyn massacre, also known as the Katyn Forest massacre , was a mass execution of Polish nationals carried out by the People's Commissariat for Internal Affairs , the Soviet secret police, in April and May 1940. The massacre was prompted by Lavrentiy Beria's proposal to execute all members of...

 of Polish prisoners by the Soviet NKVD

NKVD

The People's Commissariat for Internal Affairs was the public and secret police organization of the Soviet Union that directly executed the rule of power of the Soviets, including political repression, during the era of Joseph Stalin....

 in 1940.