14c., "fraternal relation, relationship between sons of the same father or mother," from brother + -hood; earlier was brotherhede (c. 1300), with ending as in maidenhead; and Old English had broþerrede, with ending as in kindred. The modern form of the word prevailed from 15c.
Originally "relationship of a brother," also "friendly companionship." Concrete sense of "an association of men for any purpose, a fraternity" is from mid-14c. in the Middle English word (later also "labor union," 1880s). Meaning "a class of individuals of the same kind" is from 1728. Meaning "community feeling uniting all humankind" is from 1784. Old English also had broðorscipe "brothership," broðorsibb "kinship of brothers."
What edge of subtlety canst thou suppose
Keen enough, wise and skilful as thou art,
To cut the link of brotherhood, by which
One common Maker bound me to the kind?
[Cowper, "The Task"]
Oh, the Protestants hate the Catholics,
And the Catholics hate the Protestants,
And the Hindus hate the Muslims,
And everybody hates the Jews.
[Tom Lehrer, "National Brotherhood Week" lyrics, 1965]