Well, the Mandalorians were sort of being invadery dicks - like they do every thirty years or so, apparently - and some of the Jedi were all NO WE SHOULD LET THINGS HAPPEN and some Jedi were all UH PEOPLE ARE DYING FU and so most of the Jedi that sided with protecting people ended up going all Sith and it's complicated and depressing because it involves lots of Jedi killing each other after that.