Original: Personal unions can arise for very different reasons , ranging from near coincidence ( a princess who is already married to a king becomes queen regnant , and their child inherits the crown of both countries ) to virtual annexation ( where a personal union sometimes was seen as a means of preventing uprisings ) .
Simplified: The case that a princess who is already married to a king becomes pregnant , and their child inherits the crown of both countries is a rather common cause .