The Spanish Flu was a devastating influenza pandemic that swept across the globe from 1918 to 1919, infecting about one-third of the world's population. It is estimated to have caused the deaths of 50 million people, making it one of the deadliest pandemics in history. Unlike typical flu strains, the Spanish Flu had a high mortality rate among young, healthy adults. The rapid spread was facilitated by the movement of troops during World War I, and the lack of medical knowledge at the time made it difficult to control. Its impact reshaped public health policies worldwide.