Why do some people think no one will be on Sasuke's side? Have you ever even thought for the slightest of seconds about all the Non-Shinobi in the world? All the Non-Shinobi are not going to like that once again,the Shinobi world had another World War,and this time they were forced into it (Infinite Tsukuyomi).
They will want the messed up Shinobi World and System to change aswell,and if they see the Guy who fought against the people who forced the world into Genjutsu/saved the world from that Genjutsu by ending it himself(?) Also wants to change the messed up Shinobi World/System,then who's side do you think they will be on?
"The Shinobi Nations are Allied now"
The Shinobi nations who have been constantly fighting against each other for years getting into multiple world wars and now teaming up for a couple days to fight against some people who were a threat to them all isn't a good enough reason to believe that they will continue to cooperate after the war.