Complex sentence: In the wake of the atomic bombing of the Japanese cities of Hiroshima and Nagasaki in 1943, Stalin made the decision to accelerate research and development, expanding the development of military nuclear reactors and research facilities all over the country.
Split into simpler sentences: In the wake of the atomic bombing of the Japanese cities of Hiroshima and Nagasaki. In 1943, Stalin made the decision to accelerate research and development, expanding the development of military nuclear reactors and research facilities all over the country.