The Egyptian queen Cleopatra was the immediate threat to Herod. She was ambitious to expand her domain eastwards. She successfully urged Mark Antony, her husband, to transfer to her Herod's rich palm and balsam groves at Jericho. Cleopatra even visited Judea in 34 BCE and was toying with the idea of seducing Herod — seduction being something she regularly enjoyed, according to Josephus. She may also have envisaged the bed as a trap that would expose Herod to Antony's fury and result in Judea's takeover by Cleopatra. Herod, in turn, was tempted to destroy the Egyptian queen while she was in his power. However, he abstained for fear of risking Antony's displeasure. In the end, Cleopatra unwittingly contributed to Herod's political survival. Thanks to her greed for the land of the Nabateans — in the south of modern Israel and Jordan — she persuaded Antony to launch Herod and his army against them. So he and his main forces were kept away from fighting on Antony's side against Octavian at Actium in 31 BCE.

From 37 to 4 BCE, with firm Roman backing, Herod ruled over Judea, Idumea, Samaria and Galilee, as well as over further regions in southern Syria and northern Transjordan. Not since David and Solomon in the tenth century BCE had there been a Jewish kingdom as large as Herod's, not a mean achievement for the Idumean parvenu. The first 12 years of Herod's reign (37-25 BCE) saw the consolidation of his power. He built fortifications in Jerusalem, Samaria and at Masada, silenced all opposition to his rule and eliminated his Hasmonean rivals, Aristobulus and Hyrcanus II, the brother and the grandfather of his second wife, Mariamme. The former drowned in an arranged swimming pool accident and the latter was strangled. The middle period of Herod's rule (25 to 13 BCE) is characterised by his spectacular building activities at home and abroad, culminating in the reconstruction of Jerusalem's Second Temple and the creation of the city and port of Caesarea. 

The last years of his life (13-4 BCE) were poisoned by increasingly bitter family feuds, which ultimately sprang from his marriage to Mariamme. To understand the situation, we must go back to 37 BCE, the start of the monarchy. After becoming master of Jerusalem, Herod dismissed his first wife Doris and their son Antipater, in order to marry later in that year Mariamme, the granddaughter of the former high priest/king Hyrcanus II. Not only was he passionately in love with her, but through the marriage bond with Hasmonean royalty he sought to improve his popularity with his Jewish subjects. Their bliss was short-lived, however, due to intrigue, jealousy and hatred between the female in-laws, Mariamme and her mother Alexandra on the one side, and Cypros and Salome, Herod's mother and his sister, on the other. The Hasmonean royals openly despised the "lowborn" Idumeans. The Idumeans were craftier. The infighting climaxed with a charge of adultery against Mariamme, which unhinged Herod and led to her execution in 29 BCE. 

In the following year, Alexandra, the much-disliked mother-in-law, shared her daughter's fate. Alexandra twice earned Herod's displeasure for plotting his overthrow. First, in collusion with her intimate friend Cleopatra, she arranged for Antony to summon Herod and demand that he account for the drowning of Alexandra's son, the young high priest Aristobulus, but Herod managed to extricate himself from trouble. After the execution of her daughter, Alexandra tried to seize the power for herself and Mariamme's sons, but the plan was reported to the king and revenge followed.