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This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

By spring 1950, Stalin believed the strategic situation had changed. The Soviets had detonated their first nuclear bomb in September 1949; American soldiers had fully withdrawn from Korea; the Americans had not intervened to stop the communist victory in China, and Stalin calculated that the Americans would be even less willing to fight in Korea—which had seemingly much less strategic significance. The Soviets had also cracked the codes used by the US to communicate with the US embassy in Moscow, and reading these dispatches convinced Stalin that Korea did not have the importance to the US that would warrant a nuclear confrontation. Stalin began a more aggressive strategy in Asia based on these developments, including promising economic and military aid to China through the Sino–Soviet Friendship, Alliance, and Mutual Assistance Treaty.
Output:
When did the Soviets first detonate a nuclear bomb?