For the sake of this discussion, we will assert that the United States demonstrated imperial powers during the late nineteenth century and continued to dominate the global stage through the twentieth century.
What you must decide is whether or not the US is still an empire. Why or why not? You must support your claim – you get to decide this one for yourself – and argue for it with sources, statistics, and clear statements of fact.
One final aspect of the discussion is consideration of whether or not a global empire is still possible.