Hashirama didn't have EMS at that time. Hashirama fought an MS Madara with cell pain due to overusing it and won using his strongest techniques. Hashirama thought young uchihas are capable of being a threat to him even.Lol, this post can't be any further from the truth. Hashi had already beaten Madara.....
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...and its here the decision to unite the two clans was made. Had Madara refused there, then I don't see the uchiha clan to be in any position to fight Hashirama, Tobirama and the senju clan. They would've been annihilated.