In the Shield of the Prophet DLC, you can become an active participant in the alternative history of the Soviet invasion into the Afghanistan in 1979.
And this story went like this through:
Iran's leadership is beginning to develop a plan of "exporting the Islamic revolution" in Afghanistan.
Taking advantage of the weakness of the central government of Afghanistan and the favorable geopolitical situation, in June 1979, Iran began a full-scale military invasion into the border provinces of Afghanistan.
In response, the Soviet Union began an emergency entering the armed forces in Afghanistan, in order to prevent the overthrow of the pro-Soviet government in Afghanistan.
The war begins between Iran and the Soviet Union for control of Afghanistan...
Source: The Developer Website.