In his Islamic Government (Hokumat-e Islami) — which is a collection of his lectures in Najaf published in 1970 — he rejected both the Iranian Constitution as an alien import from Belgium and monarchy in general.
He believed that the government was an un-Islamic and illegitimate institution usurping the legitimate authority of the supreme religious leader (Faqih), who should rule as both the spiritual and temporal guardian of the Muslim community (Umma).
In early 1970 Imam Khomeini gave a lecture series in Najaf on Islamic Government which later was published as a book titled variously Islamic Government or Guardianship of the Islamic Jurists (velayat-e faqih). This was his most famous and influential work and laid out his ideas on governance (at that time):
As anti-Shah regime protest grew, so did Imam Khomeini’s profile and importance. During the last few months of his exile, Imam Khomeini received a constant stream of reporters, supporters, and notables, eager to hear the spiritual leader of the revolution.
Only two weeks after the Shah fled Iran on January 16, 1979, Imam Khomeini returned to Iran triumphantly, on Thursday, February 1, 1979, invited by the anti-Shah revolution which was already in progress.
Conservative estimates put the welcoming crowd of Iranians at least three million. When Imam Khomeini was on plane on his way to Iran after many years in exile, a reporter, Peter Jennings asked him: "What do you feel?" and surprisingly Imam Khomeini answered "Nothing!"