The obvious answer: Columbus came from Genoa, in Italy, which is also home to focaccia, the northern Italian bread that may be a precursor to the modern pizza.
But that's not the answer I'm looking for. The answer is: Tomatoes!
Tomatoes came to Italy from the New World in the post-Columbus 16th Century. Technically speaking, it wasn't Columbus who brought tomatoes to Europe. The first tomatoes to reach European shores came from Peru, which was conquered by Francisco Pizzaro of Spain in 1531.
Honestly though - if I had asked "What does Francisco Pizzaro have to do with modern pizza?" wouldn't you have answered, "Who cares?"
Most Europeans feared that tomatoes were poisonous (they are members of the Nightshade family), but the adventurous (and hungry) poor of Naples found that tomatoes were not only NOT deadly, they were delicious.
And they tasted mighty fine on a hot baked flatbread. With cheese. The first pizza, as-we-know-it.