The Creation of Dioceses

I think the newest diocese in the Roman Catholic church is Mongolia, but feel free to correct me. There are many hundred dioceses throughout North Africa and the Middle East that have had their hierarchy "suppressed." I do know that in the Anglican church there are four diocese for the Middle East:

Province: The Episcopal Church of Jerusalem and the Middle East
The Diocese of Jerusalem (includes Jordan, Syria, and Lebanon)
The Diocese of Cyprus and the Gulf States
The Diocese of Iran
The Diocese of Egypt, North Africa, and the Horn of Africa

Sudan was originally part of this structure but it became its own Province.

But here you go, courtesy of New Advent, the gift that keeps on giving:

(1) Creation of Dioceses

Strictly speaking, it is only in missionary countries that there can be question of the creation of a diocese, either because the country was never converted to Christianity or because its ancient hierarchy was suppressed, owing to conquest by infidels or the progress of heresy. Regularly, before becoming a diocese, the territory is successively a mission, a prefecture Apostolic, and finally a vicariate Apostolic. The Congregation of Propaganda makes a preliminary study of the question and passes judgment on the opportuneness of the creation of the diocese in question. It considers principally whether the number of Catholics, priests, and religious establishments, i.e. churches, chapels, schools, is sufficiently large to justify the establishment of the proposed diocese. These matters form the subject of a report to Propaganda, to which must be added the number of towns or settlements included in the territory. If there is a city suitable for the episcopal see, the fact is stated, also the financial resources at the disposal of the bishop for the works of religion. There is added, finally, a sketch, if possible accompanied by a map, indicating the territory of the future diocese. As a general rule, a diocese should not include districts whose inhabitants speak different languages or are subject to distinct civil powers (see Instructions of Propaganda, 1798, in Collectanea S. C. de P. F., Rome, 1907, no. 645). Moreover, the general conditions for, the creation of a diocese are the same as those required for dividing or "dismembering" a diocese. Of this we shall speak below.