"Zinfandel is a variety of red grape planted in over 10 percent of California vineyards.[1] DNA fingerprinting revealed that it is genetically equivalent to the Croatian grape Crljenak Kaštelanski, and also the Primitivo variety traditionally grown in the "heel" of Italy, where it was introduced in the 18th century. The grape found its way to the United States in the mid-19th century, and became known by variations of the name "Zinfandel", a name of uncertain origin." - Brian Sullivan

So Zinfandel (or at least the name) is uniquely North American but is basically Primitivo. - Brian Sullivan