This is actually a theme that we can see as being key to much of the fiction of Henry James. His novels and novellas delighted in contrasting the innocence and naievety of his American protagonists with the experience, sophistication and corruption of his European characters. Thus it is that the innocent and rather naive Isabel Archer, with all of her ideas of experiencing life and living it to the full, is thrown in the path of the rather diabolical Madame Merle and Gilbert Osmond, and suffers greatly as a result. Gilbert Osmond is "unfathomable," in the words of Madame Merle, and and is able to talk rather chillingly about the way in which Isabel Archer has "too many ideas" that are all "very bad ones," which means they can be "sacrificed" easily.
In so many works by Henry James, innocence collides with experience in the form of a clash of two different civilisations meeting each other in the characters that he brings to life in his work. This novel is no exception, as the trip to Europe that Isabel Archer makes is one that will transform her for ever and cause her to mature in a way that will impact her character for the rest of her life.