Which conflict initiated the significant use of total warfare in the 20th century?

The correct choice is World War I, as this conflict marked a pivotal shift in the nature of warfare, where the concept of total war became more pronounced. In total war, nations mobilize all their resources—military, economic, and civilian—to achieve complete victory over the enemy.

During World War I, large-scale battles and trench warfare resulted in unprecedented levels of destruction and loss of life. The war saw the involvement of whole populations and economies, with governments directing industries to produce war materials and citizens participating in support roles. This era also witnessed the use of propaganda to galvanize public support and maintain morale, which exemplifies the total war approach of engaging the entire society in the war effort.

While the other conflicts listed also displayed elements of total warfare, it was World War I that laid the groundwork for these practices, establishing a paradigm that would be further developed and intensified in World War II and beyond. The comprehensive mobilization of societies during World War I significantly changed the methods and implications of warfare, making it a landmark moment in military history.