Answer:
Fighting against Romans and barbarians alike, he extended the Frankish Kingdom and consolidated its power by conquering Gaul and unifying it under the rule of his Merovingian Dynasty; his descendants would rule much of Gaul for the next 200 year.
Explanation:
The correct answer is the Influenza Pandemic.
This Influenza (flu) Pandemic killed between 20 and 100 million people (estimates differ) - more than the war itself!
The source of the Pandemic is still not known, and people suggest such places as the US, China and France.
They are most likely Libertarians.
