Ancient books are not always, if ever, easy to read properly, unless one can find helpful background information.
The Herods in the New Testament are not clearly differentiated, so we read about King Herod in Mt. 2:1(re the nativity of Jesus) then there is a King Herod in Mk. 6:18 (the one whom John rebuked for marrying his brotherâ€™s wife) and there is yet another King Herod in Acts 12:1-2(who had James the brother of John killed). Same guy? No.
The King Herod of the nativity accounts was King Herod the Great, that master-builder who was appointed puppet King of the Jews in 40 BC and who ruled as King of Judea from 37 BC until his death in 4 BC.
When Herod the Great died in 4 BC the territories under his jurisdiction were divided among his sons. So [Herod] Archelaus (called â€˜Herod the Ethnarchâ€™ on his coins) ruled Judaea and Samaria, from 4 BC to AD 6, [Herod] Antipas (called â€˜Herod the Tetrarchâ€™ in Lk. 3:19) ruled Galilee and Perea from 4 BC to AD 39 while [Herod] Philip ruled outside Israel in Iturea and Traconitis from 4 BC to AD 34. (See Lk. 3:1)
As New Testament scholar Craig Blomberg says in his Jesus and the Gospels, 1997, p. 22
, â€œAntipas is the Herod who appears at several points throughout Jesusâ€™ adult life on the pages of the Gospels (esp. Mark 6:14-29 pars.; Luke 13:31-33; 23:6-12).â€
Now the King Herod of Acts 12:1-2 is Herod Agrippa I (AD 41-44) grandson of Herod the Great via his father Aristobulus IV who was ordered to be strangled by his own father Herod the Great in 7 BC.
Interestingly there is yet another Herod mentioned in the New Testament but not by the term â€˜Herodâ€™. This is King Agrippa, one of the trial judges of Paul in Acts 26. His epithet would have been Herod Agrippa II, son of Herod Agrippa I, and his rulership as client-king of Galilee was from AD 49-92.
Now you should be able to make better sense of your reading or study of the New Testament.