War has changed in many ways since the 1940s.  Let us look at a few of the most important changes.

First, wars between major powers have essentially disappeared.  The last war that could be seen as a war between major powers was the Korean War, with China playing the part of a major power opposing the United States.  Modern wars have largely been between major powers and very minor countries or even non-state actors.

Second, wars have become more technological.  We can see this perhaps most clearly in the use of unmanned aerial drones in conflicts today.  There are also things like precision-guided munitions and much more use of technology for surveillance and information gathering. 

Finally, wars are, at least from the point of view of American troops, much more survivable.  This is partly because the wars are smaller and it is easier to get wounded soldiers back to medical facilities.  But it is also because of improvements in medicine and technology.  Soldiers today are able to survive wounds that would surely have killed them in the wars of the past.