There have been relatively few personal unions that managed to become political unions:
England, Scotland, & Ireland
France & Navarre
Aragon, Castile, & Leon
Poland & Lithuania
What other personal unions do you think could have unified politically? or at least remained unified.
Are there any alternate personal unions that would likely have unified politically?
Are there any OTL unions that were extremely unlikely to unify (personally or politically)?
etc etc
EDIT: please also expand your reasoning a little more than just an "X & Y" response