Small update on my Langobard kingdom - a kindom that rivals the Roman Empire on terms of land mass.
After the christianization the Roman Empire was more stable than ever before, so I had to rely on the migration events to grab land here and there. The Goths, Visigoths and Burgundians spawned in Southern Europe and I had to be fast to conquer them before Rome could react - sadly, these pesky Romans managed to reclaim parts of Illyria before I could force a PU on the Goths.
After itegrating them and remaing Britannian tribes, I've converted to Nestorianism. I've lost my tribal bonus, but could finally assimilate all remaining minorities.
Later the Bulgarians spawned and took a few Roman provinces in the Balkans and near Crimea with them, so I've gained new land again without challenging the Romans - who seem to have a thing for decade-lasting Interregni.
After I've finally reached the required tech level to recruit colonists, I colonized the remaining unsettled provinces in Britain, Scandinavia and the Baltics. The Moravs and Estonians, loyal allies before the christianization, had been conquered and formed into Nestorian vassal states - I've later conquered the Sapmi and re-released them with additional provinces.
The Sarmatians are in a PU with Persia - formerly the Parthian Empire - otherwise, I'd have conquered them to redistribute some provinces to the Magyars which will convert to Hungary in a few 100 years.
Xiongnu once borded Armenia, but the Parthians repeatedly crushed them in their hunger for more land, left unchecked by their historical arch enemy.