This wikipedia image highlights the ability to partition Iran into several ethnic groups, although urban areas like Tehran will pose a major problem to this (Iraq tried before, but made several miscalculations). In the North, Azerbaijan could be expanded with a Turkish population(and controlling the Kurdish region) and in the South the oilfields are in regions traditionally settled by Arabs (former region of interest for Iraq). This agglomeration is held together by a tradition of unity dating far back in time, although many of these are descendants of newer immigratory traditions that are being bandwaggoned to this proud narrative highlighted with the
and Persia - Iran has been reinvented several times in their history, each time stretching back the narrative to
. The other unifying influence is that Iran was converted to Shia and is now the major Shia country with an influential theocracy. As long as the Shia Sunni divide remains important, this provides a major glue against fractioning Iran.
It is a hard nut to crack in order to install something different there that does not pose a problem for the control of the oilfields and their pipelines. I highlighted this notorious field manual, because, while being likely a forgery, it does convincingly show actually employed techniques used for reliably guiding political entities by foreign influence - the modern concept of conquest.