a group separating from a larger one
withdrawal
a group of people in a larger group (e.g. a political party) with different views, often ones that suit their own interests
group sharing a belief or cause
the smaller number or part (of a group)
an outnumbered group
(an instance of) a division of an organization (especially Church) into two or more groups
separation
a group of people united by (especially political or religious) beliefs or opinions
school of thought