Reasons for Settlement
Adpihi was settled and named by a religious group of human colonists from Earth's sphere of influence. They had been seeking to establish a colony where they could practice, preach, and follow their religion and their customs without the scorn of non-believers or the interference of secular authorities.
(They had an Abrahamic faith -- similar to those of Judaism, Christianity, and Islam -- but similarities and differences are too intricate to go into in the present article.)
A disaster during the flight made them unsure whether or not they had made it to the correct planet. A second disaster during landing sufficiently corrupted their records that later generations were unable to prove they had come from any particular region of Earth.
(It is widely believed, however, that they set out early in Earth's "21st century C.E.".)
Order of Settlement
They first crashed on Continent 2 near its NorthWestern corner, just SouthWest of the isthmus that connects it to Continent 1, and just South of the mountain range, great lake, and river that separate Continent 1 from Continent 5.
Some of them almost immediately migrated to Continent 1 and began its settlement. Therefore the settlement of Continent 1 was barely behind that of Continent 2.
Climate, and perhaps unknown other difficulties, at first prevented them settling Continent 5; they had spread all the way East across Continent 1 to Continent 6 before they began to settle Continent 5.
Inimical wild native species at first made it impossible to spread from Continent 1 to Continent 3. But when this was eventually accomplished, they quickly spread all the way across Continent 3 and Continent 4.
Then they began regular visits across Ocean 2, from Continent 5 to Continent 3 and from Continent 2 to Continent 4.
Also, once Continents 1 and 6 were settled, people set out from the SouthEast of Continent 1 and spread across all of the islands of Oceans 1 and 3.
Once all of the inhabitable, but uninhabited, areas of a Continent or an Ocean had been shrunk below a certain size, it was considered that "its frontier had been closed".
For Continents 3 and 6, "the Closing of the Frontier" actually coincided with "Continental Unification". But, except for Continents 4 and 6, there had been various attempts to force unification which had been resisted by those who did not like the terms imposed upon them.
The Great War
From internal to Continent 5 came an attempt to unify it by force. Allied with that, from the East of Continent 1 came an attempt to unify it by force as well.
These attempts were both resisted by, among others, one of the later two great powers of Continent 1. The other later great power was, at that time, not so great -- it was the chief victim of the conqueror from the East.
One of the most important participants in the resistance was Continent 3, which was already unified. The fighting was world-wide. Most states resisted the attempts to force unification; and, when the fighting was over, these attempts had failed.
One major result of the end of the war was that Continent 3, as the largest and richest and most militarily powerful of the already-unified Continents, became globally dominant.
Another was the beginning of the first attempts at peaceful Planetary Unification.
Another was the retirement of the defeated conqueror from the East from the military field of endeavor, and the start of its eventually-successful bid for leadership in more peaceful fields.
Another was the recovery of that conqueror's chief victim and its assumption of a place as one of the two greatest powers of Continent 1.
Another was Continent 3's attempts to unify Continent 4 in partnership with it.
Another was Continent 3's attempts to unify Continent 5 in partnership with it.