Zechariah 1:1

The eighth month] the month Bul (see 1 Kings 6:38), corresponding to part of October-November. The second year of Darius] i.e. 520 b.c. This was the first Darius, son of Hystaspes, who had just succeeded to the Persian throne. Babylonia formed part of his dominions. He found the old decree of Cyrus in the archives of Babylon, permitting the Jews to return and build the Second Temple, and renewed it (Ezra 6:1). The son of Iddo the prophet] There should be a comma after Iddo. Zechariah was the prophet.

2-6. The people are warned to repent by the fate of their fathers, who suffered exile because they refused to listen to God's word by the earlier prophets.