Original: The attempted coup d'etat by Silius and Messalina had probably made Claudius realize the weakness of his position as a member of the Claudian but not the Julian family. This weakness was compounded by the fact that he did not have an obvious adult heir, Britannicus being just a boy.
Simplified: The attempted coup d'etat by Silius and Messalina had probably made Claudius realize the weakness of his position since he did not have an obvious adult heir, Britannicus being just a boy.