Old enemies of Judah and Benjamin heard that the exiles were building The Temple of the God of Israel.
They came to Zerubbabel and the family heads and said, "We'll help you build. We worship your God the same as you. We've been offering sacrifices to him since Esarhaddon king of Assyria brought us here."
Zerubbabel, Jeshua, and the rest of the family heads of Israel said to them, "Nothing doing. Building The Temple of our God is not the same thing to you as to us. We alone will build for the God of Israel. We're the ones King Cyrus of Persia commanded to do it."
So these people started beating down the morale of the people of Judah, harassing them as they built.
They even hired propagandists to sap their resolve. They kept this up for about fifteen years, throughout the lifetime of Cyrus king of Persia and on into the reign of Darius king of Persia.