Finally, the manga of Naruto has been ended, and yet I wasn't able to figure out why Tobirama created Edo Tensei. From what I've known, Edo Tensei is technique was intended for the dead to be reincarnated into soldiers able to clear a battlefield with devastating and under any other circumstance suicidal attacks.
That is correct. Edo Tensei was designed to be used as a weapon. Edo Tensei has several uses:
- Using your Enemies' allies against them has a deep impact on morale (Imagine having to fight to the death against your best friend/brother/father)
- Regenerating soldiers can use suicidal moves repeatedly (Although it does seem like some techniques leave a permanent damage, even on an Edo Tensei'd body, like Itachi's Izanami).
- Increasing your numbers is always a good thing.
Tobirama created this technique to battle in the wars between clans/villages during his time alive.