Complex sentence: The Greek position at Artemisium may have been chosen in order to watch for such attempts; if the narrowness of the channel had been the only determinant, the Allies could have found a better position near the city of Histiaea.
Split into simpler sentences: The Greek position at Artemisium may have been chosen in order to watch for such attempts. If narrowness of the channel had been the only determinant, the Allies could have found a better position near the city of Histiaea.