Conversation so far:
Who succeeded Guru Arjan ?
His choice of Arjan as successor, as throughout most of the history of Sikh Guru successions, led to disputes and internal divisions among the Sikhs.
So who won the dispute and became the Sixth Guru ?
His choice of Arjan as successor, as throughout most of the history of Sikh Guru successions.
Are there any other interesting aspects about this article?
The mainstream Sikh tradition recognised Guru Arjan as the fifth Guru, and Hargobind as the sixth Guru.

Question: Why was there a dispute about succession ?
Self-contained rewrite: Why was there a dispute about the succession of Guru Arjan ?