The Nile and the Horn
Two Christian worlds either side of the Red Sea's southern end — Kush, Makuria and Alodia on the middle Nile, Aksum and its successor in the Ethiopian highlands — which outlasted the empires that converted them and were reached by Islam last.
The line below is a time axis. Position on it is date, so concurrency is visible: concurrent polities sit side by side rather than in sequence.
3 sourced edges run between this region and another, to Saba', Himyar and Egypt, Third Intermediate Period. Those are not drawn on this line — a thread that crossed regions would assert a sequence nobody cited — but they are on each polity’s own page.