When Has the Hijri Calendar Been Accepted As the Islamic Calendar?

When has the Hijri Calendar been started to be used? When has the Hijri Calendar been accepted as the Islamic Calendar?

Since the establishment of Islamic State in Madina upto the caliphate of Hazrat Umar (ra), Muslims used to regard the dates of important events as the beginning of the calendar and determine their time according to them. (Like the Fijar War and the Last Hajj of Prophet Muhammad (pbuh))
As a result of extensive conquests in the caliphate of Hadrat Omar (ra), the borders of the Islamic State have expanded. In the extending borders, some problems have come out in a few official documents because of the absence of a calendar. These problems have convinced the Caliph to find a solution which has been needed for a long time.
Thus, in the 17th year of Hijrah, the second Caliph Hazrat Umar and the commission gathered for this issue approved the hijrah (migration of Muslims from Makka to Madina) as the era and accepted the “Hijri Calendar” as the Islamic Calendar.