Conversation so far:
What did Isabella I of Castile do in her later years?
Isabella received the title of Catholic Monarch by Pope Alexander VI
Why did Isabella I of Castile receive the title of the title of Catholic Monarch by Pope Alexander VI?
Isabella I Queen of Castile embarked on a process of spiritual unification, trying to bring the country under one faith
Was the process of spiritual unification and trying to bring the country under one faith a successful endeavor?
the Treaty of Granada was broken in 1502
Why was the treaty of Granada broken in 1502?
After a Muslim uprising in 1499, and further troubles thereafter.
What other troubles were there besides the Muslim uprising in 1499 that broke the treaty of Granada in 1502?
How did the Christians react to the muslim uprising in 1499 that broke the treaty of granada in 1502?
Muslims were ordered to either become Christians or to leave
Are there any other interesting aspects about the Isabella I of Castille article?
Isabella and her husband had created an empire and in later years were consumed with administration and politics
Why did Isabella and her husband had created an empire and in later years were consumed with administration and politics?
Isabella I and her husband were concerned with the succession

Question: Why were they concerned with the succession?
Self-contained rewrite: Why were Isabella I and her husband concerned with the succession and worked to link the Spanish crown to the other rulers in Europe?