Complex sentence: Although it gained in strength as made its way south, the Norwegian king received only lukewarm support from his Norse-Gaelic vassals--only Dubgall mac Ruaidrí and his close relatives, and Magnús himself, came out whole-heartedly.
Split into simpler sentences: Although it gained in strenghth as made its way south, the Norwegian king received only lukewarm support from his Norse-Gaelic vassals. For example, only Dubgall mac Ruaidrí and his close relatives, and Magnús himself, came out whole-heartedly.