Conjunction or Preposition? It Matters a Lot!
First, recall that to ask why, we say ¿Por qué? It is written as two words, with an accent on the last word. It sounds exactly like porque, which means because. It is a conjunction. Conjunctions are followed by clauses, with a conjugated verb. So when porque (because) is used, it will be followed by information that explains why whatever is said in the first clause happened. Notice in the following example that the clause that follows the conjunction has a conjugated verb (estaba/was):
Mi hermano se quedó en casa porque estaba enfermo (My brother stayed home because he was sick).
This word and its use is relatively easy. It corresponds to one of the English uses of because. However, the other uses of because in English often involve a preposition, such as because of -- and this little addition, as often is the case when a preposition is added, will alter things greatly when seeking a solution in Spanish. Now the concept of causality is expressed with a preposition. In Spanish, the most common solution is to use a causa de plus a noun or pronoun. Do not use porque de!
A causa de la tormenta decidimos regresar a puerto (Due to/Because of the storm, we decided to return to port).
Compramos el vestido a causa de ella (We bought the dress because of her).
When the object of the preposition is not a person, debido a -- plus a non-personal noun -- is preferred.
Dejaron la canoa en la ribera debido al trabajo de subirla al campamento (They left the canoe on the riverbank due to the trouble of carrying it up to the camp).
Finally, por is also a preposition that indicates cause: by, for the sake of, out of, or other expressions of motive:
Por su culpa, no pude regresar a tiempo (On account of him/his fault, I couldn't get back in time).
Lo hicimos por la gloria (We did it for glory's sake).