What if the completion of the Reconquista had gone differently?

Castile and Aragon take Granada, ending 780 years of Muslim rule in Iberia in the same year Columbus sails.

If it had gone differently: Spain stays preoccupied at home; there is no unified, militant, cash-strapped crown looking for a gamble across the ocean.

1. 1492Columbus reaches the Americas, The Atlantic stays a barrier for generations; Europe's empires grow east, not west.
2. 1525The Atlantic slave trade scales up, The plantation economy never finds its labour force; Atlantic colonies stay marginal.