That's a nice thought, but it is probably not the cause. "There is a steep positive slope in the numbers of battle deaths between 1816 and 1914 and a steep negative slope between 1945 and 1997." [1] Obviously, something happened in 1945 that changed everything. This change can be almost entirely explained by the United States acquisition of nuclear weapons, and the subsequent policy decision in the United States with respect to war and isolationism.
Prior to WWII, US foreign policy was one of isolationism, where the United States largely ignored other nations politics and conflicts. This policy is very cost effective as long as war is avoidable. Unfortunately, neither WWI or WWII were, and both were massively costly. In the wake of WWII isolationism was abandondoned, in part because the United States was the only nation with nuclear arms. The United States decided to take an active role in stabilization, largely through the use of nuclear deterents to prevent interstate conflict between major powers, and smaller, more frequent "stablization" conflicts.
Evidence for this is first seen less than three years after WWII ended, with the Berlin blockade, where the Soviet Union attempted to force the west into giving up control of Berlin by blocking supply access. This led to the delivery of 2,236,406 tons of supplies over 278,228 flights in eleven months (the Berlin airlift), which was enabled directly by the United States threat of Nuclear retaliation against the soviets. The United States publicly moved B-29 bombers to Britain to discourage the Soviet Union from interfering with the airlift. Had this deterent not existed, it's entirely possible that the situation would have escelated.
Less than five years after WWII ended, with the outbreak of the Korean war, the pattern is reinforced. Before the start of the war, the United States produced 120 MK-III "Fat Man" nuclear weapons yielding 18-49 Kt, and started production of MK-4 1-30 Kt bombs, of which it produced 550 by May 1951. Interestingly, all of the Mk-III's were retired in 1950, and the MK-4's were retired in 1953 because the pace of development was so fast. The US deployed additional B-29's to Britain, with bombs, to discourage the Soviet Union from entering the Korean War. When the Chinese entered the war, MacArthur intended to deploy nuclear weapons against the Chinese, in part to distrupt supply lines with radioactive fallout, and planned to destroy China until it surrendered. MacArthur also made clear that he intended to use nuclear weapons against China if they crossed the 38th parallel, and this was communicated to them. MacArthur was relieved in part because of these plans, and his belief that the power to order the use of nuclear weapons was his, and not the President's.
Ridgway, MacArthur's replacement, was authorized to use nuclear weapons in the event of major air attacks originating from outside Korea, and china was directly notified of such. The United States entered the war pre-emptively, then used the threat of nuclear weapons to prevent others from doing so, and to prevent the escaltion of the war.
It is not difficult to imagine that without these stabilizing actions either the Berlin airlift of the Korean war could have quickly escelated into World War 3. In 1954, just after the Korean war, the first thermonuclear weapon (5-7Mt) was deployed, marking an end to interstate war between major powers. The highest yielding thermonuclear weapon the US ever deployed, the 25 Mt Mk-41, entered service in 1960, but by that point, the line in the sand had already been drawn.
Since 1945 US policy has been clear, it will interfere in foreign affairs, using economic sanctions, conventional war and nuclear deterents to prevent costly large scale conflict. The direct result of this has been stabilization, a long-term decline in war deaths, and the end of interstate war between major powers. It will be interesting to see what happens as this strategy is abandoned as the survivors of WWII die off, and memory of why the US spends so much on its military fades. Hopefully enough time has gone by that a return to hostilities seems unthinkable; no doubt if there is a return, major hostilities will be massively costly in terms of life, money, liberty, and safety.
1: The Declining Risk of Death in Battle
Bethany Lacina, Nils Petter Gleditsch and Bruce Russett
International Studies Quarterly, Vol. 50, No. 3 (Sep., 2006), pp. 673-680