This is an extremely difficult matter for modern readers of the gospels to grasp, but Luke never meant for his story about Jesus's birth at Bethlehem to be understood as historical fact. Luke would have had no idea what we in the modern world even mean when we say the word "history." The notion of history as a critical analysis of observable and verifiable events in the past is a product of the modern age; it would have been an altogether foreign concept to the gospel writers for whom history was not a matter of uncovering facts, but of revealing truths.
Reza Aslan, Zealot: The Life and Times of Jesus of Nazareth
bible, history