In Iraq the losses were .44 deaths per division per day (through 2008, after which it dropped to less than .1). During the Vietnam war the average division lost 3.2 troops a day, which was similar to the losses suffered in Korea (1950-53). By comparison, during World War II the daily losses per American averaged (over 400-500 combat days) about twenty soldiers per day per division. That’s more than 50 times what divisions in Iraq and Afghanistan lost. On the Russian front during World War II, German and Russian divisions lost much more than their American counterparts did in Europe or the Pacific and often over a hundred dead a day for weeks on end.
For short campaigns, which Iraq and Afghanistan are not, the losses were similar. That's why the concept of "days in combat" is used to measure casualties over long duration. During World War II, and before and since, divisions would often be out of the combat zone for days, or weeks, before going back into action. Thus the spectacular six week German conquest of France in 1940 saw their combat divisions taking 30 dead (on average) per day. But during another spectacular military victory, the 1967 Six Day War, Israeli dead were 22 per division per day, and that actually went down to 18 a day during the less spectacular 1973 war. By contrast, the three week invasion of Iraq in 2003 saw U.S. troops suffering 1.6 dead per day per division. During the 2006 Israeli war in Lebanon, Israel lost 8 soldiers per division per day. Even the Israelis were impressed at how the Americans were able to win quickly with record low casualties.
With the dramatic drop in casualties came another big shift. In World War II, one in three casualties was killed. In Iraq and Afghanistan, only 12 percent of the casualties were fatal. This does not change the dramatic difference between combat losses then and now. In World War II, U.S. divisions suffered about 60 dead and wounded per combat day, while in Afghanistan there has been 1-2 (depending on the year) per combat day, and in Iraq 3.5 (through 2008, much less after that). So by any measure, U.S. troops have learned how to avoid getting hit. U.S. commanders see the reasons as better equipment, tactics, weapons, leadership, and training than in the past. With an all-volunteer force, the troops are smarter and more physically fit and eager as well. Many of the life-saving innovations U.S. troops have come up with in the past seven years have not gotten much publicity. Good news doesn't sell, but in this case, it has definitely saved lives.
Then there's force protection. After 1945, the 300,000 World War II combat dead reinforced Americans traditional aversion to warfare. This, despite the fact that Europeans had suffered even more in the World Wars (Russia had lost 10 million troops in World War II combat, and another 20 million soldiers and civilians to non-combat losses, while this only caused an additional 100,000 U.S. deaths). When Korea came along, the trend to take extraordinary measures to limit U.S. losses began in earnest. Some pundits point out that this force protection mania limits the effectiveness of American troops. Some soldiers and marines agree, but most are quite content to see their chances of surviving combat increased.
Keeping fatal casualties down to less than one per division per day is unique but it should not be seen as a permanent fixture. Facing a more powerful and resourceful enemy will send the rate right back up. The media doesn't like to report it but the troops will tell you that their Iraqi and Afghan foes are often incredibly stupid and do dumb things that U.S. troops usually avoid. By comparison, fighting North Korea would be much more difficult. The terrain of Korea (lots of steep hills and narrow valleys) makes it hard to use mobile warfare. The North Koreans have spent half a century digging fortifications into the sides of those hills. But morale in the North Korean army is fragile, as is the command and control systems used to run the army. North Korea can be beaten but not while having only one or two soldiers killed per division per day. It might be something closer to ten times that, depending on a lot of things you can't quite put your hands on. Like surprise, unexpected tactics, and good information about what shape the North Koreans are in. But that won't be the loss rate during a long (several hundred days) war. Without external support from Russia or China, North Korea has to fight a short war.
The important thing to remember is that while lower casualties for the better prepared force is a historical fact, experiencing historically low losses every time is not. For that reason, professional military planners in many nations are carefully studying the U.S. experience in Iraq and Afghanistan. But so are U.S. planners, who fear that American troops, now so well prepared to fight irregulars, might find themselves unprepared to fight a more conventional war and take higher casualties as a result. That is true, to a certain extent. But the major advantage American troops have gained is combat experience. They know how to operate effectively under fire. If U.S. troops are given several months to practice the specific tactics required for fighting a conventional war, they will be a formidable, combat experienced, force.