1
general::
Phrase(s): take sides
to choose one side of an argument. • They were arguing, but I didn’t want to take sides, so I left. • I don’t mind taking sides on important issues.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Also, take someone's side. Support or favor one party in a dispute, as in Parents shouldn't take sides in their children's quarrels, or Thanks for taking my side concerning the agenda. [c. 1700] Also see TAKE SOMEONE'S PART.
American Heritage Idioms