Hashirama's greatest contribution was establishing Konoha and signing the employment system with the Land of Fire's Daimyo family, helping the Land of Fire become one of the Five Great Nations.
Other nations and Shinobi forces followed suit, annexing noisy small countries, eventually forming the Five Great Nations and their buffer states.
The First Great Shinobi War and Second Great Shinobi War were the processes of the Five Great Nations clashing and colliding.
As the intensity of the wars rose, cities changed hands repeatedly, and scripts, languages, customs, and systems collided and assimilated in the blood and fire.
When the mountains and rivers are broken by slaughter, one realizes shared roots and coexistence; when lives are devastated by battle, one understands the need for unification.
In the original work, Sasuke had the idea of unification.
But after being talked out of it by Naruto, he abandoned that idea; the revolution that should have been sparked by the battle at the Valley of the End was all bark and no bite.
The world structure didn't change; it was the same after the war as it was before!
Daimyos were still Daimyos, and commoners remained commoners for life; the Hokage's son became the Hokage, and the scapegoat's son remained a scapegoat.
The Five Great Nations remained, and the five largest military groups remained.
It was only because the Ōtsutsuki Clan, an enemy from beyond, drew the attention of the great nations that they allied with each other.
As soon as the Ōtsutsuki crisis is resolved and Naruto and Sasuke die, the conflicts between the great nations will be brought back to the table.
Because human souls are bloodthirsty, constantly engaged in struggle and slaughter.
Splitting, unifying; splitting again after unification, and unifying again after being split for a long time.
History is like a loop, a spiraling upward loop.
Constantly repeating the same things as it moves forward.
Hashirama could have accelerated the transition; with his powerful Wood Release, he could have defeated the other four nations.
But a forced unification would inevitably cause massive casualties; unification is impossible without wiping out the Shinobi Villages, Daimyos, and aristocratic groups of the great nations.
Hashirama's personality was not that of such a person.
Madara could have, but Madara skipped this inevitable historical law.
He wanted to end this constantly advancing world loop and place the world in a static, beautiful state.
A world without conflict, without slaughter, where everyone can find happiness.
Fundamentally solving the struggle within the human heart—this is a revolution that completely changes historical laws, and it's also going against the Will of Heaven.
He was too impatient! He wanted to see a world without struggle too badly!
The Slug Sage asked Hashirama, "Lord Hashirama, if you could do it over again, would you have let Madara go back then?"
Hashirama rubbed his head and gave a silly smile. "I suppose so! Because Madara is my best friend; I feel like he's my brother."
"I killed Madara in the battle at the Valley of the End, and I've lived in immense guilt ever since."
"My heart was unburdened when I woke up and heard Madara wasn't dead. That kid Madara actually faked his death to trick me back then!"
Looking at Hashirama, the Slug Sage couldn't help but reveal the truth: "Lord Hashirama, actually, you and Madara are brothers!"
"Huh?! What on earth did my father do?!"
Hashirama was shocked!
The Slug Sage quickly explained, "No, it's not Lord Butsuma's fault!"
Hashirama was even more shocked, even doubting himself: "Then it was Uchiha Tajima's... Could it be that I am—"
The Slug Sage was speechless; the successive reincarnations of Asura were never particularly bright.
"It's like this, Lord Hashirama: you are the chakra reincarnation of Asura, the ancestor of the Senju Clan, while Madara is the reincarnation of Indra."
"Indra and Asura were originally the sons of the Sage of Six Paths; they were brothers."
"The older brother, Indra, was a genius. He was the source of the Sharingan and inherited the Sage of Six Paths's immense dōjutsu power from birth."
"He invented Hand Signs and laid the foundation for Ninjutsu; he is the true ancestor of Shinobi."
"Because of his innate powerful strength, Indra was an absolute believer in power, thinking the strong could dominate the weak at will."
"In contrast, the younger brother Asura was much more mediocre, but through his own hard work and the assistance of his companions, he gained power rivaling his brother's."
"He realized that love is the key to achieving peace."
"The rift came from the Sage of Six Paths's favoritism. When the Sage of Six Paths was nearing the end of his life, he chose Asura to inherit Ninshu and passed the Six Paths Power to him."
"Indra refused to accept this result, and the two sides began a confrontation that lasted for a thousand years."
"The chakra of Indra and Asura would possess the descendants of their respective clans."
"In your era, Indra's chakra possessed Madara, and Asura's chakra possessed you, Lord Hashirama."
"So, Lord Hashirama, your feeling wasn't wrong. You and Madara restrain and influence each other; you are brothers and rivals by destiny."
(´⊙ω⊙`).
Hashirama looked at the Slug Sage in extreme shock. He hadn't expected that he and Madara really were brothers—not by blood, but brothers of destiny.
No wonder Hashirama felt a stirring of emotion the first time he met Madara; there was a bond that could never be severed.
Hashirama rubbed his head and said, "But what does that prove? Even if Izuna were resurrected, he wouldn't be able to persuade the current Madara."
"He wants to drag the world completely into a dream and end all conflicts forever."
"No—"
The Slug Sage shook her head. "That's not what I meant. What I'm trying to say is that you and Madara, Lord Hashirama, are the reincarnations of Asura and Indra respectively."
"You are brothers and rivals of destiny. Indra will not surpass Asura by too much; you influence and fulfill each other."
"When one side becomes stronger, the other will as well."
Every generation of Asura and Indra has influenced and fulfilled one another.
Asura is as strong as Indra is; they are evenly matched.
For example, with Naruto and Sasuke: just after Sasuke lost his brother and awakened the Mangekyo, Naruto learned Senjutsu.
Naruto's whole family died, and soon after, Sasuke's whole family died as well.
Naruto's IQ isn't high, and Sasuke isn't much smarter than him either!
In the original work, after Hashirama was resurrected, he couldn't match Madara because Asura's development relies on the power of companions.
Hashirama didn't have that much time to grow.
But now, Hashirama has the opportunity to be personally taught Yin-Yang Release by the Slug Sage and obtain the Six Paths Power.
The Slug Sage said to Hashirama, "Lord Hashirama, you must believe in yourself. You are the only one who can stop Uchiha Madara."
Hashirama looked at his hands with some confusion. "Me? How am I supposed to stop Madara? I already killed him once for the sake of the Village."
"Must I become his enemy again for the sake of the Shinobi World?"
"After my death, the Five Great Nations system I spearheaded went through three Shinobi World Wars. I don't know how my descendants are supposed to save this world."
The Slug Sage looked at the somewhat confused Hashirama; the Hashirama of the past would never have been confused.
No matter what he did, he would do it with determination. For instance, teaming up with Madara to establish Konoha, even when Tobirama said killing Madara would end all strife.
Hashirama still let Madara go and established Konoha with him.
But after his death, the balance he had maintained quickly collapsed, followed by mutual slaughter.
The facts were right there, negating all the efforts Hashirama had made.