Complex sentence: Its territory was combined with that of another khanate ceded by Iran, the Nakhchivan Khanate; this newly established Russian administrative territory was named the "Armenian Oblast", and was composed of the former Erivan and Nakhchivan Khanates ceded by Iran.
Split into simpler sentences: Its territory was combined with that of another khanate ceded by Iran, the Nakhchivan Khanate. This newly established Russian administrative territory was named the "Armenian Oblast", and was composed of the former Erivan and Nakhchivan Khanates ceded by Iran.