ok, so we are tlking ancient eh??
1. battle of guandu, an army of 700,000 defeated by 70000 due to fierce tactics and diversion strategy, both sides fought very fiercely
2. battle of chibi, two navies go ahead in a battle in which more than 400,000 participated in the yantze river, fierce in spy works and grusume naval battles, in the end a fire attacked ended it all in whcih the northern side was annilated