Warring States Period

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

During this time period, the average life-span was a scant 30 years for both shinobi and civilians alike. However, the biggest loss in the era was the thousands of conscripted children in the individual clans which were forced to fight in the front lines, often slaughtered by the more experienced adults which lowered the overall life expectancy. Hashirama lost his brother Itama Senju and his clansman Kawarama Senju in this era, while Madara Uchiha lost upto three of his four brothers.

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 several battles which end in a draw. 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 had to steal his brother's eyes, gaining a Eternal Mangekyō Sharingan to keep fighting his former 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 Konoha was formed.

Trivia

 * The Era of the Warring Clans could be named after the or Warring States Period, a time when Japan was in civil war and the demand of ninja was high. This moment in history was the time of many of famous ninja, including Sasuke Sarutobi. But after the war resolved, their services almost no longer needed in a united Japan, ninja faded into history.