So another f*ck-up by Hiruzen?
Uchiha Massacre
Hyuga Affair (Neji's father dying and Hirzuen basically letting Ay make unreasonable demands and threaten war)
Letting Oro escape after his experiments on dozens of villagers and 60 babies.
Invasion of Konoha by Oro.
Letting Danzo do whatever he wanted
Not doing as much as he could to have Naruto celebrated as a hero. Which he stated was the Fourth Hokage's sacrifice was for.
Yeah, I could totally see Hiruzen waifing on protecting an allied nation.
MAdara may be a better option
And they said Tobirama was the worst.
Because, the way Tobirama treated the Uchiha led to the Uchiha massacre to occur
Tobirama died when Hiruzen was still a young man, and the Uchiha Massacre happened with Hiruzen and Danzo were 64. We really can't blame Tobirama for that. Hiruzen admits he didn't carry out Tobirama's will and from what we know of the Uchiha Massacre; Hiruzen waifed on decisively putting an end to the premature stages of the Uchiha's coup.
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Even though Hiruzen himself + ANBU + Jonins could've stamped out the Uchiha without much effort.