5%, 25%, 50%

When I am thinking about the US's role in the world I like to keep 3 percentages in mind: 5%, 25%, 50%.

5% - percentage of people in the world who live in the US
25% - percentage of world oil that the US consumes
50% - percentage of world spending on defense that the US spends

Other percentages are fairly close:
6% of total land on earth
21% of total world GDP
50% of total spending on health care

To generalize, the US has about 1/20 of the total world space and people, consumes 1/4 of the world's resources (as well as produces 1/4 of total output), and spends 1/2 of the world's expenditures on defense and health care.