Recently, I started to read about history as a hobby like I used to when I was a kid. I realized that reading about "generic history" does not do it for me anymore. Instead I have some particular interests that I would like to follow up on, but I do not know where to begging.
Are there examples of two or more medieval kingdoms trying to unify/merge? Yet, they failed to do so because of internal strife, internal resistance, or cultural/religious differences?
From what I remember, I know that kingdoms merging because of marriage or free association was rare. I also remember that there was something about Queen Mary I of England marrying the heir apparent to the crown of Spain, Philip, in 1554, but that is about it.
Any interesting examples, that I could read about (with literature recomendatiosn if poossible)?