In Japan the greatest cause of casualties was the atomic bombs and the napalm bombs (which did more damage and killed more people than the A bombs).
In Germany and Europe the aerial bombing and the invasion of Europe by the Allied Forces use of Tanks and automatic machine guns caused the most casualties.
In the Pacific the total combined use of planes, ships and infantry with all their weapons caused the most casualties on both sides. Torpedo use was another factor in the Pacific for many ship deaths.
Another factor to consider is that casualties from the battles did not kill as many people as disease, exposure to the elements/climates, starvation, suicide and genocide, murders and mistreatment of the POWs did. In fact, the worldwide influenza killed more people worldwide than battle injuries.
Russia
World War II had the greatest number of casualties caused directly and indirectly by war. The death toll is listed at 84,589,300 for all countries jointly that were involved in the war. The American Civil War had the largest number of United States casualties, listed at 625,000.
In WW1 Disease.
Russia suffered the greatest in casualties during World War II. Russia lost almost 11,000,000 humans during this war event.
Russia suffered the greatest number of casualties during World War I, with estimates of military and civilian deaths ranging from 3 to 4 million. The Russian Empire faced immense losses due to battles on the Eastern Front, civil unrest, and famine exacerbated by the war. These casualties significantly impacted the country's social and political landscape, contributing to the Russian Revolution in 1917.
modern weapons
If the war was before the event of antibiotics, the greatest losses were due to infections.
Russia
Russia suffered the greatest loss of life during World War I. There were thousands of casualties on all sides suffered during the war.
The Civil War
the flamer caused over 300 deaths in world war one
World War I resulted in around 20 million casualties, while World War II had approximately 70-85 million casualties. This means that World War II had a significantly higher number of casualties compared to World War I.
World War II had the greatest number of casualties caused directly and indirectly by war. The death toll is listed at 84,589,300 for all countries jointly that were involved in the war. The American Civil War had the largest number of United States casualties, listed at 625,000.
In WW1 Disease.
Russia suffered the greatest in casualties during World War II. Russia lost almost 11,000,000 humans during this war event.
I wouldn't call any war "great" but WWII is the largest war in history in terms of of area of the world affected and people involved, and the worst in terms of the number of casualties.
World war Two, Russian had over 10million casualties.