We've got the story.
Looking for "peace" , Madara and Hashirama met at that river , they created the concept of konoha here , it was their answer , unify clans in "villages".Clans is one side , village the other side , they're on the same side.
After creating Konoha , they understood that their answer was good but incomplete , seing that the war between clans is soon replaced by the war between villages ( the love of your clan is replaced by the love of your village , your comrades ).Your friends are still being killed by other shinobis.
How to get world unity?
Madara have an answer , Hashirama haven't but he knows he doesn't like Madara's.
There they became rivals to find the answer.And Madara left Konoha.
Madara came back to get Hashirama DNA , and lost .
When wars grow bigger , shinobis grow stronger , to a point that the globe was at stake during their fight.
Hashirama had still no answers , he couldn't kill Madara , he followed Madara's idea , resurect the Juubi to make the world unify against that weapon.
I never saw a pound of hatred in Madara's face.
If Itachi understood Madara's plan , he would have done exactly what he has done ( stop the coup d'état in Konoha , go help Madara's plan , give his strenght to somebody who will fight the beast ) .