Joseph & Mary went to Bethlehem because it was the "City of" this king & Joseph came from his lineage
[DOC] [TLE] Luke 2:4 So Joseph also went up from the town of Nazareth in ... [PAR] Joseph also went up from Galilee, from the city of Nazareth, to Judea, to the city 
of ... which is called Bethlehem; (because he was of the house and lineage of 
David:) ... Joseph, a descendant of King David, went to Bethlehem because 
David had ... 5He went there to register with Mary, who was pledged to him in 
marriage... [DOC] [TLE] Luke 2:4 Commentaries: Joseph also went up from Galilee, from the ... [PAR] And Joseph also went up from Galilee, out of the city of Nazareth, into Judaea, to 
the ... which is called Bethlehem; (because he was of the house and lineage of 
David:) ... To be enrolled with Mary  Who also was a descendant of David: his 
... Christ was born at an inn; he came into the world to sojourn here for awhile, as 
at... [DOC] [TLE] Did a Census Really Bring Joseph and Mary to Bethlehem ... [PAR] 4 And Joseph also went up from Galilee, from the town of Nazareth, to Judea, to 
the city of David, which is called Bethlehem, because he was of the house and 
lineage of David, 5 to be registered with Mary, his betrothed, who was with child."