Kori Schake describes  Paul Ryan’s foreign policy in a post that does an impressive job of not telling us anything specific about it:
Representative Ryan does seem to have a predilection for basing his policy choices on “foundational principles.” Just as his arguments for putting our entitlement programs on sound footing are tied to the bigger ideas of what kind of future we want our country to have, his arguments for our foreign policy are tied to what kind of world we want to live in — the bigger ideas of advancing freedom and helping build institutions that preserve it.
This is another way of saying that Ryan often speaks in vague generalities and abstractions when he makes these arguments. If there are guiding principles to Ryan’s foreign policy, they seem to be 1) an aversion  to “moral relativism” and 2) the belief  that “it is always in the interest of the United States” to promote American political principles in other countries. These two are linked together, and Ryan believes that the one follows from the other. If one makes exceptions to the latter, that is proof of one’s “moral relativism,” which others would call prudence and discernment. Another way to describe this “principled foreign policy” is simplistic and often detached from reality.
In practice, this means that he tends to disapprove of policies that rely on cooperation with states that do not “share our values.” He seems to place more importance on whether another state “shares our values” than he does on whether its cooperation is useful in advancing concrete U.S. interests. For instance, Russia and the U.S. may have common interests that are served by such cooperation, but Ryan regards this cooperation as “appeasement,” and he seems to view it this way in part because of the character of the Russian government.
Idealism matters to Americans because, in truth, nearly all our wars are voluntary and our citizens are difficult to motivate to war. We are much more comfortable making the world safe for democracy, ending fascism, and advancing our values than we are risking our sons and daughters for causes that are difficult to square with the kind of society we want to live in ourselves.
Schake accepts that the purpose of idealistic and moralizing foreign policy rhetoric is to generate public support for “voluntary” (i.e., unnecessary) foreign wars. In fact, most Americans are wary of putting soldiers at risk for intangible, ill-defined goals, and they tend to be more skeptical of wars that are being waged in the name of “making the world safe for democracy” and “advancing our values.” Most Americans don’t see this as the purpose of U.S. foreign policy or as a proper role for the U.S. military. Moralizing rhetoric can sometimes be useful for trying to justify “causes that are difficult to square with the kind of society we want to live in ourselves,” which is why interventionists rely so heavily on it when they are arguing for illegal and aggressive wars. Even so, Americans tend to be least supportive  of foreign wars that are based mostly or solely on idealistic or “humanitarian” grounds. Initial support for the invasion of Iraq was as high as it was because the public was wrongly led to believe that Iraq posed a significant threat to American security. Wars that have no real connection to perceived U.S. interests, such as Kosovo and Libya, have received much less support.