 Operation Barbarossa was the largest military operation in human history — more men , tanks , guns and aircraft were committed than had ever been deployed before in a single offensive . A total of 75 percent of the entire German military participated . The invasion opened up the Eastern Front of World War II , the largest theater of war during that conflict , and it witnessed titanic clashes of unprecedented violence and destruction for four years that resulted in the deaths of more than 26 million people . More people died fighting on the Eastern Front than in all other fighting across the globe during World War II . 
