The 20th century witnessed several significant health crises that impacted global populations. Notable events include the Spanish Flu of 1918, which infected about one-third of the world's population and resulted in millions of deaths. Other crises included the emergence of HIV/AIDS in the late 20th century, which led to widespread health challenges and social stigma. Additionally, outbreaks of diseases such as polio and tuberculosis prompted public health initiatives and vaccination campaigns. The century also saw the rise of antibiotic resistance, which poses ongoing challenges to modern medicine. These health crises shaped public health policies and responses worldwide.