Florence Nightingale's environmental theory emphasized the importance of the physical environment on patient health and recovery. The theory stated that nurses should control and alter environmental factors like ventilation, warmth, cleanliness, noise and diet to support the patient's natural healing process. Nightingale developed this theory based on her experiences as a nurse during the Crimean War, where she observed the impact of the hospital environment on patient mortality rates. Her theory shaped the development of modern nursing by establishing the role of nurses in managing the patient's physical surroundings.