Is The New Art of Defense in Chess or The Art Defense in Chess better? I am 1900 on an upward trend.
Yes, the new book is quite different to the old one:
On the whole, however, The New Art of Defense in Chess should be seen as a fundamentally new book. This is because Soltis recognizes the way in which dynamism and activity have become fundamental to modern defensive techniques.
Source: ChessBookReviews, emphasis is mine.
Synthesising the review, the reasons why the book is different is because:
- Computer analysis has helped players find flaws in the attack in postmortems, which they use to improve their defensive technique
- Players are more open to playing 'ugly', counter intuitive moves that are based on concrete analysis
- After Tal's reign as world champion, players realised that active defensive is usually better than passive defence