Those numbers are very inaccurate, first of all, Europeans have been constantly at war, and remember Chinese population is actually about the same if not less as Europe during the early periods.
It was only late in time that we begin to become a more populous country. There are many reasons, but let say war is one of them, but disease is another and a host of other things.
Second, you got to remember, when a Chinese "source" say a million, the reality is closer to a hundred thousand if that. For example, Germany mobilized millions to attack Russia and millions crossed the border, while Nationalists China say a million, in reality, less than 200,000 actually saw action, if that. They just counted troops that exists rather than troops that actually were deployed.
Third, Europe's constant warfare resulted in famine, and all sorts of disasters, but the fact that they been constantly happening is one reason, the over all number of these dynastic wars must be around the same as Chinese numbers.