The Second Great Ninja War was the second of the four great wars, involving the majority of the shinobi villages and countries. Not much is known about the politics of this era, but there were known conflict between Konohagakure, led by the Third Hokage, Sunagakure, likely led by the Third Kazekage, Amegakure, led by Hanzo of the Salamander, and Iwagakure, presumably led by the Third Tsuchikage.
The majority of the fighting seems to have taken place in minor countries like Amegakure, leaving them devastated. The eventual outcome of the war seems to have been in favor of Konoha. Nagato referred to it as a war Konoha started.