Because and because of
Because means ‘for the reason that’. It is a conjunction. It is used at the beginning of a clause.
Because of is a two-word preposition. It means ‘by reason of’, ‘on account of’. It is used before a noun or a pronoun.
Compare:
We couldn’t go out because it rained.
We couldn’t go out because of the rain.
Position
Because and its clause can go either before or after the main clause.
I did it because he told me to do it.
Because he told me to do it, I did it.
