En 1898 estalló la guerra entre España y EEUU a causa de la voladura del crucero yanqui "Maine". El hecho quiso hacerse pasar como casual y fue el que sirvió de pretexto.
Well, I can't stop myself from pointing out one thing first: it is "crucero", with c.
After that, the thing is that "hacerse pasar" is an idiom, so it cannot be separated. "hacerse pasar" means "to impersonate", or to pretend to be.
el hecho quiso hacerse pasar como is translated as something like
The fact was wanted to be presented as
It's preferred on this site that you show us what you've tried so far, to figure things out, and also that you specify which part is causing you trouble -- where exactly your confusion is.
But in this case I can see several things going on that make this sentence not very straightforward.
First, hecho here means "act" or "incident." (In other contexts, it often means "fact.")
You may also be getting tripped up on the idiom
which is often translated as "impersonate" -- kind of like how, in the early days of Hollywood, a light-skinned African American actor might pass for white, so as to avoid being limited to playing stereotyped servile roles. Or how Jews in the early days of Nazism in Germany were able to pass for Gentile. Here, it means "to be passed off as."
The se has been explained well elsewhere on this site and I wouldn't be able to explain it as well as they have.
Next, casual is a bit of a false friend in this sentence. Here, it means "accidental."
So, literally (but this will sound weird), the sentence is saying, The incident wanted to pass itself off as an accident, and was that which served as a pretext.
(Pretexto means a justification which was not the true reason or cause.)
Putting it all together, we get:
El hecho quiso hacerse pasar como casual y fue el que sirvió de pretexto. | The incident was passed off as an accident, and was what was used as the pretext [for war].
It still doesn't quite make sense, though. As I understand it, the explosion was probably an accident, but those in the US who wanted to go to war used the incident to their advantage. They accused Spain of having blown the ship up in an act of aggression. But if someone with a solid mistrust and (well placed, in my opinion) paranoia about U.S. agents provocateurs might arrive at a vague idea that maybe the US itself caused the ship to blow up.
Bottom line: I wouldn't get into a nitpicky discussion about this sentence with anyone in Latin America about this sentence. It's an emotional topic -- and understandably so.