One of the mysteries of life is the alliance between Islamist extremists and leftists such as Trotskyist revolutionaries. According to their dogmas they are violently opposed to each other, but everywhere such extremists are to be found giving each other mutual support. This is disguised by the tactic of adopting organisation names which obscure their origins and instead invoke some universal good. For example they will claim to be Anti-War (who isn't?) whilst in reality supporting the most brutal war-makers around. Whatever the answer, understanding this 'Unholy Alliance' will shed light on what truly motivates these extremists.
Horowitz's book does not do too much to explore the causes of this bizarre phenomenon but it does a fantastic job of documenting it and will be an eye-opener to almost everyone who reads it, even if already rather well-informed.
In my opinion it would be foolish to be active in politics these days without a good understanding of the topic Horowitz covers. I recommend this book most highly.