There are two possible options for the main campaign for IB II (IB for M2TW):
410AD campaign - essentialy the BI campaign made for m2tw (only possible because hordes are in m2tw)
Tetrach campaign - A campaign which would start at the end of the 3rd century AD and focus on the 4 roman empires,
it would include - 4 roman factions, the franks, the visigoths, the ostrogoths, and other factions.