Why was Jesus born during Roman occupation?

Some objected that because Christ came to grant liberty to His people, it was not fitting that He came at a time when the Jewish people were subjected to Roman occupation and the Herodian dynasty (Herod was not a true Jew). 

St. Thomas answered that because Christ came in order to bring us back from a state of bondage to a state of liberty, it was fitting that He be born into bondage with us and then lead us out. We can grasp this logic in a wider sense when we consider that He assumed our mortal nature in order to give us an immortal nature; He died in order to restore us to life. St. Thomas, referencing Bede, wrote that Christ submitted Himself to bondage for the sake of our liberty. He also added that Christ wished to be born during the reign of a foreigner so that the prophecy of Jacob might be fulfilled (Genesis 49:10): The scepter shall not be taken away from Juda, nor a ruler from his thigh, till He come that is to be sent. The bondage was not to be ended before Christ’s coming, but after it and through it.

Summa Theologica, Part III, Question 35, Article 8.