In 1918, a new influenza virus emerged. During this same time period World War I was taking place. The conditions of World War I (overcrowding and global troop movement) helped the 1918 flu spread. The vulnerability of healthy young adults and the lack of vaccines and treatments created a major public health crisis, causing at least 50 million deaths worldwide, including approximately 675,000 in the United States. Below is a historical timeline of major events that took place during this time period.