Why did the influenza epidemic of 1918 spread across several continents?

Several factors contributed to the widespread transmission of the 1918 influenza epidemic across multiple continents:

Global Mobility: The early 20th century saw a significant increase in global mobility due to advances in transportation, particularly steamships. People traveled extensively for trade, work, and migration, making it easier for the virus to spread across borders and oceans.

World War I: The ongoing World War I played a critical role in facilitating the spread of the virus. Millions of soldiers from different countries were mobilized and transported to various fronts, creating ideal conditions for the rapid transmission of the virus among large populations. Soldiers lived in close quarters, often in unsanitary conditions, promoting the spread of respiratory infections.

Lack of Immunity: Human populations had no prior immunity to the 1918 influenza virus strain, making them highly susceptible to infection. The virus was unusually virulent and infectious, and it is estimated that about one-third of the world's population was infected during the pandemic.

Inadequate Healthcare Infrastructure: The healthcare systems of the time were generally unprepared to handle such a severe pandemic. With limited medical knowledge, inadequate medical facilities, and shortages of doctors and nurses, many affected regions struggled to provide effective care for the overwhelming number of patients.

Global Communication and Awareness: While communication was slower compared to modern times, news and information about the disease did spread across the globe through print media, telegraph, and other communication channels. However, the fragmented nature of communication and a lack of centralized coordination hampered effective international cooperation in controlling the spread of the disease.

These factors combined to create the conditions for the devastating global pandemic that transpired during the 1918 influenza epidemic, resulting in an estimated 50 to 100 million deaths worldwide.