Florence Nightingale's defining achievements in modern nursing include the establishment of professional nursing standards and the introduction of sanitary practices in healthcare. During the Crimean War, she drastically improved conditions for soldiers, significantly reducing the death rate through her emphasis on hygiene and proper care. Nightingale founded the first secular nursing school, the Nightingale School of Nursing, at St. Thomas' Hospital in London, pioneering nursing education. Her work laid the foundation for modern nursing practices and the role of nurses in patient care. Nightingale's advocacy also promoted the importance of data analysis in improving health outcomes, marking her as a revolutionary figure in healthcare.