There are a lot more people today, too. Of course war death tolls will be larger.
Anyway, according to the previously cited wikipedia article, the Three Kingdoms War, the deadliest ancient conflict, took toll of 40M people. but that happened over 96 years. That's 416k per year and 0.2% of global population at that time.
WW2 caused 14M deaths per year which was "just" 0.07% of global population.
Not sure how accurate these numbers are.