Conversation so far:
What did Isabella I of Castile do in Isabella I of Castile's later years?
Isabella received the title of Catholic Monarch by Pope Alexander VI.
Why did she receive this title?
Isabella and Ferdinand embarked on a process of spiritual unification, trying to bring the country under one faith.
Was this a successful endeavor?
Treaty of Granada was broken in 1502.
Why was it broken?
After a Muslim uprising in 1499, and further troubles.
What other troubles were there?
Muslims were ordered to either become Christians or to leave.
How did the Christians react?
CANNOTANSWER.
Are there any other interesting aspects about this article?
they were concerned with the succession and worked to link the Spanish crown to the other rulers in Europe.
Why did they do this?
they were concerned with the succession.

Question: Why were they concerned with the succession?
Self-contained rewrite: Why were Isabella I of Castile and Ferdinand concerned with the succession of the Spanish Crown?