Complex sentence: In spite of the hopes placed in the Federation, the insurgency in Aden escalated and hastened the end of British presence in the territory with the British leaving Aden by the end of November 1967.
Split into simpler sentences: In spite of the hopes placed in the Federation, the insurgency in Aden escalated and hastened the end of British presence in the territory. With the British leaving Aden by the end of November 1967.