Conquering the Land of Birds and the Land of Bears was a collective decision by the leadership of Konoha and the Land of Fire. The daimyo of the two small countries had performed unremarkably; there were no other civilians, but they were also worried about their own rule.
Meanwhile, the Land of Fire's rule and development in the Land of Rain were flourishing, attracting many civilians from nearby. The Land of Earth stationed large numbers of ninja at its borders to prevent civilians from fleeing.
Sunagakure paid no attention to this at all and repeatedly evaded the Daimyo of the Land of Wind's orders. The hundred million ryo he gave Sunagakure each year was already exceedingly generous, but over the past three years, the Daimyo of the Land of Fire's Residence had provided nearly two hundred million ryo a year at minimum. Although that was less than Konoha received, Sunagakure simply could not refuse it.
As for the Land of Birds and the Land of Bears, their daimyo had little power and feared that a mass exodus of civilians would affect their rule, so they adopted the most foolish method: strictly forbidding their civilians from fleeing and killing anyone who violated the order.
This naturally enraged the Land of Fire and Konoha. Besides, the Uchiha Clan was not the only one seeking military merits. Who would not want such an easy war, where they only had to take Biochemical Mechanical Warriors out for a stroll?
Hyuga Hiashi proposed it, and ninja clans such as the Inuzuka Clan and the Aburame voiced their support. Even civilian-born ninja eagerly suggested it to Nawaki, and the war was approved just like that.
However, Konoha discovered traces of the Third Hokage and Minato Namikaze in the Land of Bears. Subsequent ANBU investigations revealed that