There is a theory that Royal Families are connected by blood even if his/her father is a royal family member from another country; international marriage between Royal Families was common, for that reason, female-line dynasty change was smooth.
王族の国際結婚が盛んで、父が他国の王族であっても血縁は繋がっていることが多かったため、女系による王朝交代が円滑に行なわれたのだとする説もある。