The opening verses of Luke 2 outline the circumstances that account for the birth of Mary's baby in Bethlehem (as opposed to Nazareth). It all started with Augustus; he decreed a census. Instead of census officials going door-to-door, everyone had to return to their hometown. Joseph was a descendant of David, and so he had to go to Bethlehem, the town of David. Mary went with him.
Three kings. Augustus, David, and Jesus. And the greatest of these is Jesus.
David was a great king. Augustus was a great emperor. But they both pale in comparison to the King of kings. His earthly life and trappings were far more humble than theirs, but when he comes in his glory, David will bow, and Augustus will, too. He whose birthplace was determined by them will determine their respective fates.