The kingdom of Ostava slowly grew along the rivers of Western Keltia. The city states formed a loose network of alliances that steadily grew in strength over years. Osismied attacked Paris and angered the Ostavans. King Derfel then gave them a good reason as to why he attacked them and Ostava agreed to help them against the Frenks.
After that, when the Ostavans attacked Eastern Frenkia, the plunder from the first village was enough to supply the mercenary armies to conquer Ostava. And they did.
Ostava was the first nation in Northern Keltia to follow the Faith.