Do we know how Senju Hashirama died? The wiki says that Hashirama died shortly after the creation of Konohagakure.  Do we know how he died?  I mean, he was powerful enough to stand up to Madara, so I feels like it would be no small thing that could kill him.
It's unknown exactly how did he die, but here's what we can find. His wiki page says:


   Hashirama died shortly after the founding of Konoha in one of the many
 wars that were raging during this revolutionary era, but not before
 passing on the title of Hokage to Tobirama.1


However, if we head to the Konohagakure wiki page, we will find a more specific note:


   Hashirama died during the First Shinobi World War, necessitating his
 brother Tobirama Senju replace him as Second Hokage.1 Tobirama would
 also die during the war, appointing his pupil Hiruzen Sarutobi as his
 successor before sacrificing himself to ensure his pupils' escape from
 Kumogakure's ninja.2


Now, here's what we know about the First Shinobi War (emphasis mine):


   The First Shinobi War was the first of the great wars that involved the majority of 
 shinobi villages and countries. The war started not long after the system of one shinobi 
 village per country was established by the founding of Konohagakure. To try and
 maintain a balance of power, the First Hokage divided the tailed beasts among the 
 other five villages3 when he began his peace talks with them.


So it indeed looks like he died in the First Shinobi War, which is not too surprising, considering that


   his brother - the Second Hokage Tobirama Senju - died in the same war2, in which other Kages and Tailed Beasts were involved.





1 Character Databook 1, page 116 
2 chapter 481 pages 4-10
3 chapter 404 page 14