But despite the pitiful state into which the country had descended, the major outside powers, Russian and the Ottoman Empire, did not intervene as they had in 1722-1725.  It was partly that they were busy elsewhere, and surely also that the outcome of their previous attempts had not encouraged them to repeat the experiment.

That is from Michael Axworthy’s A History of Iran: Empire of the Mind, a good general introduction to the history of the country.