I’m trying to really dive deep into European history. I was recommended the aforementioned titles, which one would you recommend I start with? I plan on reading them both. I’m looking to read the easier one first, then I’ll move onto the other one. Thank you!
Edit: for clarity, The Celts by Nora Chadwick, The Ancient Celts by Barry Cunliffe.
Chadwick's book is by now very out-of-date, it was published in 1970, and scholarship is significantly different now than it was when the book was written. Cunliffe's book (being from 1997), is far more up-to-date, though it must be stressed that some of the theorising in the book around the development of the Celtic language family as an Atlantic-fringe lingua Franca has its detractors in the linguistic community, and the books has received some criticism for its embrace and perpetuation of older scholarly views about the Celts rather than being skeptical of them.
Cunliffe's book is absolutely your best bet out of the two, though if I may I might suggest John Collis' 2003 book The Celts: origins, myths, and inventions as a companion to any big popular work you might read on the subject,, its not a big book, and does a very good job of explaining why the idea of "The Celts" developed the way it did and what the problems with using the label are.