In World War II, the average tank engagement was about 700 meters, but it took an average of 18 shots to knock out another tank. During the 1973 Arab-Israeli war, the average range was about a kilometer, and it only took two shots to destroy the target. But by the 2003 invasion of Iraq, the average range was over two kilometers, and it took a little more than one shot per kill. The wars in Kuwait, Israel and Iraq were unique, however, in that they were fought in a generally flat, desert like terrain (meaning there was little vegetation.) A large part of World War II was fought in urban or wooded areas, where the longest shot you could get, under any circumstances, was about half a kilometer. However, the increased accuracy of modern tanks makes their gun more lethal no matter what the range. But longer range means that enemy crews with less training, and less capable fire control equipment, are less likely to get off an accurate shot. And increasingly, the first shot is the one that will kill you.
Bombing accuracy has also made enormous gains. During World War II, you had to drop about nine thousand bombs, from an altitude of 10,000 feet, to guarantee a hit on 60x100 foot target. You had to stay that high to avoid most of the anti-aircraft fire. Back then, accuracy (Circular Error of Probability, or CEP) was one kilometer (meaning that half the bombs dropped would fall into the one kilometer circle.) By the Korean war (1950-53), CEP had improved to 330 meters, meaning it only took 1,100 bombs to hit the target. A decade later, during the Vietnam war, CEPs of about 120 meters were achieved. This meant only 176 bombs, were needed. By the 1991 Gulf War, the average CEP was 60 meters, and 30 bombs, were needed. In 2003, the CEP was less than ten meters, and one bomb, and one aircraft, was all it took. During World War II, it required over 500 aircraft to get the hit, which is why back then, most of the bombing was either with hundreds of bombers, or a much smaller number of bombers coming in very low (and very likely to get shot down if the target was heavily defended).
In the last two decades, the U.S. Army has emphasized marksmanship. This means that infantry, machine-gunners and tank crews are much more accurate than they have been in the past. This is a major reason why anyone fighting American troops takes such high casualties. While most opponents fire wildly, American troops fire back with deadly accuracy. All of these changes, and the American dedication to marksmanship, has greatly upset the leaders of many foreign armed forces. The highly accurate tanks and bombs require money. Not just for the equipment, but for the cost of wear and tear on equipment, and ammo used, for lots of training. Most nations keep defense costs down by not using their weapons a lot, and not firing off a lot of ammo. But this has increasingly led to catastrophic defeats at the hands of more accurate and better trained troops like the Americans (or British, or troops of any army that train a lot.)
For decades, the Soviet Union built weapons that were not sturdy enough to be used a lot for training. These tanks, guns and other weapons were meant to be taken care of until there was a war, then they were used a lot, in the hope that a quick victory could be achieved. Now that the Soviet model has been, well, disgraced, many generals, and admirals, are being forced to rethink over half a century of accepted wisdom.
Combat continues to become more of a distant, but deadlier, experience. The recent campaigns in Afghanistan and Iraq have reminded military commanders world wide that trends in how wars are fought over the last three centuries are continuing, and accelerating. Three hundred years ago, in the early 18th century, gunpowder (in muskets and mobile cannon) had extended the range of weapons beyond what any army had ever seen before. That was just the beginning, as over the last three centuries, weapons have achieved longer range, and greater accuracy. This has forced armies to spread out. By a century ago, it was often necessary for armies to spread out over many kilometers of frontage. For thousands of years before that, a few hundred meters of front was the most two armies would encounter. But with rifles and artillery able to hit with increasing accuracy, at every longer ranges, troops had to spread out, and keep their heads down. No more standing tall and marching into battle.