Complex sentence: It was therefore entirely reliant on foreign areas (particularly the provinces of North Africa, Asia and Egypt) inside the empire capable of shipping adequate amounts of grain to the capital (60 million modii) and for the provincial populations that did not produce grain.
Split into simpler sentences: It was therefore entirely reliant on grain supplies from foreign areas inside the empire (particularly the provinces of North Africa, Asia and Egypt). These areas were capable of shipping adequate amounts of grain for the population of the capital (60 million modii) and for the provincial populations that did not produce grain.