Okay people i am not bashing Hashirama but he powerful shinobi.
The uchiha clan and the senju clan faught each other many times.Other ninja allainces hire the uchiha clan to fight the senju because they were a good match against them.If Madara and Hashirama faught each other many time during war but non have die but when Hashirama become hokage or konoha reunite Hashirama finally beat Madara and taught he die.
The reason why Hashirama beat EMS Madara because as a hokage,they must get all the information of jutsu of clan in their village and enemy.Remember Hiruzen office had tones of information of jutsu ,which Orichimaru (before leaving konoha) stole/read .
Another question why the senju never conquer any clan like the uchiha did in the past?The senju deceitful wanted to become friend with uchiha to win other clan.Izuna worn him when hashirama explain his dream.
It stated here Madara (not hashirama) use his powers to take one clan after another clan.Hashirama basically use Madara power to build konoha and also exterminate the uchiha clan eventually.