The following is the Oct. 25, 2021, Congressional Research Service In Focus report, Defense Primer: Geography, Strategy, and U.S. Force Design.
From the report
The United States is the only country in the world that designs its military to depart one hemisphere, cross broad expanses of ocean and air space, and then conduct sustained, large-scale military operations upon arrival in another hemisphere. The other countries in the Western Hemisphere do not design their forces to do this because they cannot afford to, and because the United States is, in effect, doing it for them. Countries in the other hemisphere do not design their forces to do this for the very basic reason that they are already in the other hemisphere, and consequently instead spend their defense money primarily on forces that are tailored largely for influencing events in their own local regions of that hemisphere. (Some countries, such as Russia, China, the United Kingdom, and France, have an ability to deploy forces to distant locations, but only on a much smaller scale.)
The fact that the United States designs its military to do something that other countries do not design their forces to do can be important to keep in mind when comparing the U.S. military to the militaries of other nations. For example, the U.S. Navy has 11 aircraft carriers while other countries have no more than one or two. Other countries do not need a significant number of aircraft carriers because, unlike the United States, they are not designing their forces to cross broad expanses of ocean and air space and then conduct sustained, large-scale military aircraft operations upon arrival in distant locations.
As another example, it is sometimes noted, in assessing the adequacy of U.S. naval forces, that U.S. naval forces are equal in tonnage to the next several navies combined, and that most of those several navies are the navies of U.S. allies. Those other fleets, however, are mostly of Eurasian countries, which do not design their forces to cross to the other side of the world and then conduct sustained, largescale military operations upon arrival in distant locations.
The fact that the U.S. Navy is much bigger than allied navies does not necessarily prove that U.S. naval forces are either sufficient or excessive; it simply reflects the differing and generally more limited needs that U.S. allies have for naval forces. (It might also reflect an underinvestment by
some of those allies to meet even their more limited naval needs.)
Download the document here.