An SF book in the alternate history sub-genre ( if there is such a thing?)  It  was written the late19 80s or ealy 90s and based on the question - what if the muslims had won the great battle in Spain in the 14th centry and had gone on to rule the world instead of the catholic-christians?  Unfortunately I can't remember either the title or author, but hope some of you knowledgeable ones  can come up with something.  Thanks for any and all help!! 

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Was it an actual novel or a short story? I've read a bunch of short stories with that general idea, and a couple with that specific branching point. Maybe try a search here ( www.uchronia.net ) and see if any of those sound familiar.

Years of Rice and Salt, by Kim Stanley Robinson?

Are you perhaps thinking of 'Lion's Blood' and 'Zulu Heart' by Steven Barnes?  It's 2002, though.  A good read!

Here's the amazon review of 'Lion's Blood':

Amazon.com In the year 1863, a primitive village is raided, the men killed, and the women and children captured. The survivors find themselves chained in the dark, filthy hold of a ship crossing the ocean to the New World, where they are sold into slavery. The powerful master of a vast Southern plantation purchases the 11-year-old Irish lad Aidan O'Dere. Yes, you read that right--in this alternate America, the South was colonized by black Africans, and the North by Vikings, who sell abducted Celts and Franks to the Southerners. Through his brilliant inversion of our history, author Steven Barnes examines the complex evils of slavery in a new light with Lion's Blood, an intelligent and exciting novel of freedom and bondage, battle and intrigue, sex and love, set in an America threatened by total war as Aztecs, Zulus, Moors, and whites clash.

Thank you one and all for the great tips, I'll check them all out - especially the "Uchronia" link.  That is truly an awesome site.

The Years of Rice and Salt by Kim Stanley Robinson involves 99% of the european population being wiped out by the Black Death. Muslims and Buddhists end up running the world, and the Chinese discover America, completely by accident. The main characters keep meeting each other in the afterlife and discussing where they  went wrong before the next reincarnation. Excellent book, absolutely fascinating!