Question: what is the biggest military campaign in history?
Answer: Khalid ibn Walid. ... 
Frederick the Great. ... 
Conquest of Gaul. (58 BC) by Caesar.
March across the Alps. (218 BC) by Hannibal.
Defeat of Persia. (334 BC – 329 BC) by Alexander.
Mongol Invasion of China. (1218 – 79)
Defeat of the Third Coalition. (1805) by Napoleon.
Fall of France. 1940.