would have known not knew

[ostap77]

"BUCK did not read the newspapers, or he would have known that trouble was
brewing, not alone for himself, but for every tide-water dog, strong of muscle
and with warm, long hair, from Puget Sound to San Diego."

This is an extract from a Jack London's writing. Why would he use "would have know"? Did he mean to say that since he hadn't been reading the newspapers he didn't know and couldn't have known that trouble was brewing? Would it be possible to change "would have known" to "didn't know" in this context? Do we use nowadays "trouble is brewing"?

 

[Munch]

"Would have known" tells us more than just "didn't know". Buck didn't know because he didn't read the newspaper. The newspaper would have told him if he had read it.

"Trouble is brewing" is a phrase I hear very rarely in conversation. However, I would not be surprised to find it in a modern newspaper or novel, for example. It is not archaic in my opinion.