A civil war started, with one one side
Cassius, the murderers, and on the other side
Octavian. Antony and Octavian won.
But in 40 BC the Romans lost Judea again. The Parths conquered Jerusalem and cut off the ears of the High-priest Hyrcanus. According to the Jewish law he was now mutilated and could be no longer High-priest. Antigonus, son of Aristobulus II now became leader and High-priest. Herod fled to Rome.
In 39 BC he was appointed king of Judea by the Romans. He still had to conquer it, and so he did, supported by the Romans. In 37 BC Jerusalem was besieged and conquered again, and another massacre followed.
Herod married Mariamne, the sister of Hyrcanus, the last of the Jewish kings of Judea.
Because of that he got a certain legitimity.
Herod was a loyal subject to the Romans, who did not interfere with his goverment. He built temples for the Roman gods and for emperor Augustus, the adopted son of Julius Caesar (but not in Jerusalem). After him Herod named the new constructed port Caesarea. After Mark Antony (the one of Cleopatra) he named the new castle in Jerusalem Antonia.
Paul was brought to this castle (Acts 21).
Herod was a respected man in the Roman empire: once he was the chairman of the Olympic Games.
At the same time Herod tried to be a pious Jew. In Jerusalem no heathen temples were built, although he built a palace for himself, a theatre and a hippodrome, a rece-course for horses.
In 19 BC he strated rebuilding the Temple. He did everything not to irritate the Jews. He took care that all necessary materials were ready for use (some feared he might stop half-way) and trained priests to become building constructors. Only they were allowed to built the holy parts of the new Temple. At the same time he took care that the sacrifices were not interrupted.
The temple became the most beautiful building of that time.
More pilgrims than ever came to this temple. Sometimes more than half a million.
The familiy-life of Herod was not happy. He had his wife Mariamne and three of his sons killed from fear of conspirations.
Augustus said about this: At the court of Herod it is safer to be a pig than a son.
When he died, probably in 4 BC the state was divided among his remaining sons.
According to Matthew Jesus was born during the goverment of Herod.