"The fortress that 'All My Sons' lays siege to is the fortress of unrelatedness."

Joe's biggest problem hinged on the fact that he couldn't see himself as related to everyone..... he saw himself as unrelated. Thus, his goal to provide his own sons with what he considered a good life superceded any thoughts of others. His sons were more important than the sons who died because of his defective parts.... the money and security was more important than his neighbor's child.....  In the end, he realizes that they were in fact, all his sons. Hence the title.