Conversation so far:
When did Ruhollah Khomeini return to Iran?
Ruhollah Khomeini returned to Iran on 1 February 1979
Why did Ruhollah Khomeini return to Iran?
Ruhollah Khomeini decided to return to Iran after Mohammad Reza Pahlavi, the Shah of Iran, fled on 16 January 1979.
How'd Ruhollah Khomeini get back to Iran?
A welcoming committee was formed on 21 January 1979, to organise and ensure Ruhollah Khomeini's return.

Question: Why did they allow him back in?
Self-contained rewrite: Why did Iran allow Ruhollah Khomeini back in?