The Uktena and Wendigo refer to the European tribes as the Wyrmcomers, as they unknowingly brought Eater-of-Souls with them when they came to the Americas. Eater-of-Souls was only banished back to Malfeas by the sacrifice of the entire Croatan tribe.
The 11 non-American tribes also took over many caerns that once belonged to the Uktena, Wendigo, and Croatan. While some were vacant because of the Croatan's sacrifice, many more were taken over by the European tribes because they were hungry for places of power. They fought with the native Garou and won through superior numbers.
The European Garou did not, by and large, actually bring Wyrm-creatures with them, they merely followed them there from Europe. But the Wyrm-creatures that came with European settlers ravaged the the Pure Lands. The European Garou then blamed the Uktena and Wendigo for not stopping this and attacked them and took their territory.
The Uktena have overcome some of their bitterness towards the other tribes, but the Wendigo still harbor great resentment towards the European tribes. The Get of Fenris, Silver Fangs, Shadow Lords, and Fianna are most likely to be called Wyrmcomers, as they were the ones to most aggressively expand into new territory and take caerns from the native Garou.