This visualization by Information is Beautiful shows the major causes of death for the 20th century.

According to the data in this graphic, the most common causes of death were non-communicable diseases (excluding cancer) such as cardiovascular diseases, diabetes, respiratory diseases, neuro-mental illness, and digestive illness; infectious diseases such as smallpox, diarrhea, malaria, tuberculosis, and respiratory diseases; death caused by humans such as murder, war, suicides, air pollution, drugs, and accidents; health complications, and cancer.