Warring States Period

Before the village system was established with the founding of Konohagakure by the Senju and Uchiha, the was an extremely bloody period in history where the hundreds of individual shinobi clans fought in constant, bitter warfare.

History
During this time period, the average life-span was a scant thirty years for both shinobi and civilians alike. However, the biggest loss in the era was the conscripted children in the individual clans which were trained to fight on the front lines, and were often slaughtered by the more experienced adults which lowered the overall life expectancy. Such losses included Hashirama and Tobirama losing their brother Itama, and their clansman Kawarama Senju in this era, while Madara Uchiha lost up to three of his four brothers.

With battles breaking out at any given moment, there heavy casualties to the world and in an attempt to become stronger, some clans such as the Hagoromo clan forged an alliance with the Uchiha.

Both Hashirama and Madara, along with their respective younger brothers Tobirama and Izuna, grew and become infamous leaders of their respective clans. Despite the friendship they made as children, Hashirama and Madara engaged each other in a number of battles, with Madara's survival enhancing his own reputation as a legendary shinobi. But during this time, Madara and Izuna discovered the secret of the Sharingan; becoming the first two Uchiha to awaken the Mangekyō Sharingan after killing their comrades. During these constant battles with the Senju clan, Madara's vision degraded further and further until he was near blindness. Acquiring his brother's eyes and integrating them into his own, he gained an "Eternal" Mangekyō Sharingan to keep fighting his friend and rival during the war at cost of suffering his clan's Curse of Hatred.

However, after decades of fighting, most of the clans in the Land of Fire, under the Uchiha and Senju banners formed a first lasting truce after being bled dry. The only person who opposed the peace was Madara, who argued for the Uchiha clan to continue the fighting but was persuaded to join in a permanent alliance with the Senju clan, and Konohagakure was formed. This set a precedence which others soon followed suit, creating the Five Great Shinobi Countries, as well as some smaller, outlying villages and settlements.