Original sentence: During the war, his native Estonia was successively occupied by the Soviets, Germany and again the Soviets.Even after he resumed a relatively normal life and chess career, however, his play at the highest level appears to have been affected by living under the enemy occupation of the Soviet Union, which at a minimum must have aggravated the stress of playing under the watchful eye and tight control of the Soviet chess hierarchy.It was expected that the winner of this tournament would be the challenger for the World Champion title, in a match against World Champion Alexander Alekhine, but the outbreak of the Second World War, especially because of the first occupation of Estonia by the Soviet Union in 1940–1941, brought negotiations with Alekhine to an end.Keres participated in several tournaments in Europe under the German occupation, and when the Soviets occupied Estonia in 1944, he attempted to escape.With the Nazi-Soviet Pact on August 23, 1939, Estonia was occupied by the Soviet Union on 6 August 1940
Edited sentence: During the war, his native Estonia was successively incorporated into the USSR, then occupied by Germany and after that liberated by the Soviets and became the part of the USSR again.Even after he resumed a relatively normal life and chess career, however, his play at the highest level appears to have been affected by watchful eye and tight control of the Soviet chess hierarchy.It was expected that the winner of this tournament would be the challenger for the World Champion title, in a match against World Champion Alexander Alekhine, but the outbreak of the Second World War, especially because of the first incorporation of Estonia into the Soviet Union in 1940–1941, brought negotiations with Alekhine to an end.Keres participated in several tournaments in Europe under the German occupation, and when the Soviets liberated Estonia from Nazi occupation in 1944, he attempted to escape.With the Nazi-Soviet Pact on August 23, 1939, Estonia was incorporated into the Soviet Union on 6 August 1940