Probably because one belong to alliance and other didn't?

Because one fought for alliance, and other for his own purposes. It's such a common sense, i don't know how to even explain it. Never thought there will be a need to explain such anime. If you misunderstood anime series, it should be hard for you to watch normal movies...

Np ^^ It's just if someone helped it doesn't mean they are allies. Like Orochimaru and saske organization helped too in GNW (i don't remember how they were called). Could find similar scenarios in all anime series.