Eh, give it a few years, another major world war or 2... badda-bing-badda-boom.
War isn't a significant cause of death versus the number of deaths each year anyways. Look at the
stats on wiki. ALL intentional deaths (not even just war, also including murders) is only 2.84% of world deaths. WWII was about 70 Million over 6 years, which is statistically significant, being that for 2002 there were ~57 Million deaths, so add 10 to that, plus the fact that there were less people in the 1940s, then ya, War would be BIGGER, but unless we're talking about NUCLEAR war, war is not, and will not be a major cause of population decline.
Contrast this to the Spanish Flu (you know, a REAL pandemic, not this imitation crap from last year), that killed 50-100 million people in under a year. And the Black Death which took out somewhere between 30-60% of Europe's population.
Nuclear war (and the resulting famines/breakdown in services) could really reduce population, but not regular wars. I'd bet on disease/famine for likelyhood (if it happens at all) of human population reduction.