I'm not so sure about that. The statistics show otherwise, early Three kingdom period's destruction caused a decline in population by over 50%. While the Wei population census show 32 million people. All together its estimated that all of China during the height of the Age of fragmentation had around 52 million men. An incerase from the 3 kingdom period, which probably had no more than 30 million.
One cannot really accurately measure the level of destruction caused by warfare using the population censors. The population censors are not reliable. Just because a lot of people were not registered on the censors does not mean they were all killed by war. I hope you are not suggesting 50% of the entire population of China were killed as a result of warfare during the Three Kingdoms Period.
There are very few historical records of large scale massacres during the Three Kingdoms Period, but plenty of records for such brutal events during the Age of Fragmentation. Many died when the Xiongnu first sacked Chang'an and Luoyang, for example.