The divergence occurs in the last decade of the 15th century, when, shortly after the successful end of the Spanish Reconquista, Jewish communities in Spain and Portugal start facing increasing oppression from the royal authorities. In the 1470s, Portuguese sailors discovered the archipelago of Sao Tomé, just off the coast of western Africa. In 1493, Álvaro de Caminha received a charter to settle São Tomé and establish sugar plantations, but initially, there were few people willing to settle there and help with the colonization effort. The Portuguese crown deported several thousand Jewish children whose parents were either unable to pay the head tax or refused to do so. Most of these children died soon after arrival, but hundreds of them survived and married into the slave population that was brought from the African mainland to work the sugar plantations. Reports from the Inquisition indicate that some São Tomese were practicing Judaism as late as the 18th century, and many of the mestizos who are a majority in São Tomé today may have Jewish blood.
So, where does the divergence come into this?
Actually, the TL has an unusual narrative structure. There is not one, not two, but three divergences… and all of them occur in different ATLs. That's right : The TL actually plays out like 4 separate TLs, each showing a different fate of the Jewish descendants on Sao Tomé. To quote Jon: “…the first scene is OTL, the others follow from three of the PODs suggested in the comments” (of the original discussion thread).
Hence the title of the TL: Four scenes, four different TLs, all centered on Sao Tomé and the story of its people… Jon explains further:
“Story 1 is OTL - the New Christians did eventually fade away, but the Inquisition complained about continuing Jewish practices (and lax enforcement) on São Tomé well into the 17th century, so they lasted more than a hundred years. In scenario 3, I'd expect them to last at least as long - there will be more attention on them due to their greater social prominence, but they're also better organized for cultural transmission - but you're probably right that they're doomed in the end. I could see story 2 as a continuation of story 1, if the sugar crops fail after 1496 (although I'd envisioned timeline 2 as one where the red-rot came with the original sugar cane plantings in 1493-94 and couldn't be eradicated, causing the settlement to be abandoned). Story 4 is your POD in which Manuel becomes king earlier and colonizes São Tomé with free Jewish families, and so will not lead to timeline 2.”
You can read Four Scenes from Sao Tomé here.