While the other four great shinobi villages still believed Konoha knew nothing and were busily drawing up their battle plans, Konoha had already stationed two army groups each in the Land of Rain and the Land of Iron.
The reason for choosing the Land of Rain and the Land of Iron was that both the Land of Wind and the Land of Earth bordered the Land of Rain, allowing the armies of Iwagakure and the Hidden Sand Village to rendezvous there at any time and adjust their battle plans.
The Land of Grass and the Land of Waterfalls were only suitable for the Hidden Sand Village to fight alone, while the Land of Rivers was only suitable for Iwagakure to launch an attack alone. After discussing it, Kazekage Reto and Tsuchikage Ishikawa decided to form one massive army group, assemble directly in the Land of Rain, and launch an all-out assault on the Land of Fire.
As for the Land of Lightning and the Land of Water choosing the Land of Iron as their battlefield, that was mainly because both countries were farther from the Land of Fire. Two small countries separated the Land of Lightning from the Land of Fire, but only a stretch of sea separated it from the Land of Iron.
As an island nation, the Land of Water could only land in the Land of Bears or the Land of Iron to attack Konoha. But the Land of Whirlpools bordered the Land of Bears. If the Land of Water chose to land in the Land of Bears, it would first have to face the ninja of the Land of Whirlpools.
Uchiha Izuna's First Army Group and Senju Tobirama's Second Army Group were stationed in the Land of Iron with the First Column, Second Column, Third Column,