Original sentence: These claims to Celticity are rooted in the the historical existence of Celtic traditions in these regions and also from the fact that numerous Celtic tribes settled in the Iberian Peninsula (see Celtiberians) and left their mark, culturally and genetically
Edited sentence: These claims to Celticity are historically justified and derive not only from the long-term existence of Celtic traditions in these regionsbut also from the fact that numerous Celtic tribes settled in the Iberian Peninsula (see Celtiberians) and left their mark, culturally and genetically