It appears that way, but remember that the 20th century is also the most populous century. As a fraction of the total population killed, the 20th century is (probably) the most peaceful.
Add onto that on many levels both wars were enhanced by scarcity... Germany want more in both, the assassination of the Archduke was encouraged on by a poor economy, Hitler couldn't have rose to power without a major economic crisis, there were so many failings in production and trade that might have prevented or mitigate either war.
Not aging and not dying will certainly be an economic boon. People can work longer, experts can more deeply master their fields and there will be less loss in passing knowledge down to successors. So economic production will rise and almost certainly faster than it does with aging and death.
Then the emotional factors in war and death... If people stop dying and live to see one war, they just might carry those lessons for the rest of lives.
