In 1908, Britain's interest in Persia increased greatly after the discovery of oil there. Persia didn't have the capital to develop its own resources, so Persian rulers began granting concessions to Western businesses.
I promise that my empire will not extend pass the Khyber Pass
In 1921, Britain agreed that its empire will not extend beyond the Khyber Pass, which borders eastern Afghanistan. The Soviet Union then signed a nonaggression pact with Afghanistan.
Sounds good to me. Now if you don't mind, I have to go make peace with the Soviet Union.