Final answer:
The existence of a large upper class is not an explanation for the relative absence of class conflict in the United States; factors such as high standards of living, social mobility, and cross-cutting allegiances play more significant roles in mitigating such conflicts.
Step-by-step explanation:
The explanations for the relative absence of class conflict in the United States' historical experience include several factors, except the existence of a large upper class. The other provided reasons, such as a relatively high standard of living for all Americans, a great deal of upward social mobility, and many cross-cutting allegiances that interfere with class solidarity, have contributed to mitigating class conflict. A significant upper class would not necessarily prevent class conflict, and indeed may exacerbate it by highlighting economic disparities. Instead, factors such as belief in the American Dream and the idea that through hard work, anyone can improve their socioeconomic status, have more commonly been cited as reasons for the reduction of class-based strife.