Student or Learner
Is it correct to say "My major (or minor) was in history"?
You don't have to use the "in" when you are using major as the noun.
I majored in Communications. I minored in Psychology.
My major was [in] Communications. My minor was [in] Psychology.
But yes, it's correct.
(And as always, American usage.)
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.