Something happened which caused him to lose his fortune.

Or, of your three, only the final alternative is possible; the first two are wrong.

Sure, that also works.

I prefer "caused" here, where it's not a simple effect as in "made him leap up in terror" or "made him think again". "To cause" seems to me to fit better with "losing his fortune", which is a slower, more indirect or complex process, and also something that happened to him rather than something that he actively did.

#4 +1

#6 Vielleicht so: resulting in him losing his fortune