One interesting note, as weapons have gotten more lethal, the death rate in battle has gone down drastically. There may be a temporary bump such as the US Civil War when tactical changes have not yet caught up to technological advances.
But overall the death rate has gone down slightly.
“T.N. Dupuy has calculated the effects of weapons as their killing power is affected by changes in a number of objective factors such as rates of fire, number of potential targets per strike, relative incapacitating effect, effective range, muzzle velocity, reliability, battlefield mobility, radius of action, and vulnerability in order to calculate what he calls a Theoretical Lethality Index for each weapon that specifies its lethality power. But such objective factors, when calculated against the single variable of dispersion, change radically in their ability to produce casualties under actual battlefield conditions. The result is that, when measured over time, the measurable casualty effects of modern weapons paradoxically result in far less casualties when measured against the weapons of the past.
Dupuy notes that when measured against the nongunpowder weapons of antiquity and the Middle Ages, modern weapons, excluding nuclear weapons of course, have increased in lethality by a factor of 2,000. But while lethality has increased by a factor of 2,000, the dispersion of forces on the battlefield made possible by mechanization and the ability of fewer soldiers to deliver exponentially more firepower has increased by a factor of 4,000! The result, as Figure 1 demonstrates, has been that wars since 1865 have killed fewer soldiers as a percentage of the deployed combat force than was the case in previous wars. Except for the Napoleonic wars which utilized the tactical field formation of the packed marching column, every war since 1600 (Table 1) has resulted in fewer and fewer casualties as a percentage of the committed forces for both the victor and defeated.”
You can read the whole article here.