The theme of isolation is vast. It all depends if you are using it for comparative or single text.
Isolation works on a number of factors: 1. Isolation imposed upon Alec 2. Self-imposed isolation
1. Isolation imposed on Alec: This is created by Alicia. As she states Alec is not to go to school but remain home schooled as she does not want to be alone in the house with Fredrick. As a result of this Alec is isolated from his peers. The result of this is he becomes socially inept. When Alec does manage to find a friend in Jerry, Alicia tries to isolate them by first telling Alec he must stay away from Jerry, secondly taking Alec to Europe and thirdly sending him off to war. While Fredrick does not have much say in what is going on he does agree with Alicia when it comes to Alec having to stay away from Jerry. This means imposed isolation of Alec from both parents. Also while Alec has no love for his mother he does show awkward affection for his father. Alicia creates isolation between the two of them when she tells Alec that Fredrick is not really his father. We see the effect it has on Alec when he struggles to communicate with his father after this.
2. Self imposed Isolation When Alec goes to war there is one remark that shows Alec is isolating himself from others. Major Glendinning remarks that Alec is not mixing with the other officers and orders him to do so. This is something Alec is unable to do and shows no desire to do so.
It is arguable that Alec’s isolation is related to his sheltered upbringing and his social awkwardness. As a result with Jerry sentenced to death Alec has no one left and is in a sense isolated. He sees his only option as following Jerry in death.