World War One dominates the history of the 20th century. Its effects were felt long after it ended. Its uneasy outcome paved the way for a second and worse conflict. World War One had many bloody battles and campaigns, but in this essay I will discuss which battle was the most important. Which battle was the most important one in World War One? The theme of the war was a huge military effort that involved many battles and about 70 million soldiers, 9 million of which were killed. It is extremely difficult to decide which battle is the most important due to these factors. Of the many impo