The number of people killed in all wars is estimated to be in the hundreds of millions. The exact number is unknown due to the lack of comprehensive records and the fact that many wars have not been well documented. Additionally, the definition of a "war" can vary, making it difficult to determine which conflicts should be included in the calculation. Some of the most devastating wars in history include World War I, World War II, the Vietnam War, and the Korean War, with estimates of the death toll ranging from several million to tens of millions for each conflict.