Alexander the great
The Persians were defeated by Alexander the Great and hellenization of the Jews began in earnest. Trade and commerce and everything else came to be conducted in the Greek language. It was inevitable that this culture found its way into the homes of ordinary Jews, especially the upper and the middle classes.
The adoption of the Greek culture, especially by the priestly aristocracy led to a gradual decline in Jewish identity and inevitably with time, the entire Jewish people would have been thoroughly assimilated. Fate, however, had other plans for the Jewish people, as we shall soon see.
The sudden death of Alexander the Great in 323BC led to in-fighting among his generals, which eventually led to the division of his empire among them. For our purposes, two of these divisions are of especial interest: the Ptolemaic and the Seleucid. Egypt and its environs, including Palestine went initially to the former while Syria, Turkey and Persia went to the latter. Several years later, the Ptolemaics lost Palestine to the Seleucids. The former were benign rulers and allowed some degree of religious autonomy, but with the latter, hellenization was more thoroughly advanced.