Back when Israel had been destroyed by Assyria, the king of Assyria had taken the Israelites out of Samaria and replaced them with other people.  Now, as the people of Judah had returned to Jerusalem and had begun rebuilding the city, the people in Samaria wrote a letter of accusation against the people in Jerusalem.  They told the king of Persia that the people in Jerusalem were not going to pay taxes and would rebel against Persia once their city was rebuilt.  As a result, Artaxerxes, the king of Persia, made the people in Jerusalem halt work on the temple.  Work finally resumed during the reign of Darius.