Foreign policy without principle is dead on arrival
Most of the big problems that define the world today -- international terrorism, international relations between states, nuclear weapons, runaway climate change -- are really problems of principle, or really, lack of principle.
When was the last time that a politician in a major country wanted something done because it was tied to a larger principle? I don't mean religious pandering, which is usually identified by its empty gestures and platitudes. I mean a genuine, civilized principle about how the world should work.
In the 2000s, Americans got a lot of "principle-based" foreign policy based on the ridiculous notion that "democracy" and "freedom" were worth undertaking various invasions of sovereign states, including Iraq. So it could be the case that Americans are sick of principle-based policies.
But maybe the problem is that we need better principles. Any political principle that justifies invading another country in violation of law is not really a principle. It is more like an excuse, and a rather horrible one.
For example, when it comes to terrorism, one principle would be "the rule of law": we should treat terrorism as a crime, and put in place international rules designed to police and interdict international terrorists. Terrorists ought to be captured where possible, charged with an offense, given a lawyer and a legitimate opportunity to mount a defense before a neutral judge, and then sentenced accordingly.
The moment you find a principle, solutions start to present themselves. If terrorism is a crime, then civilized countries should be building a framework to allow for honest and rules-based prosecutions of suspected terrorists. Information and intelligence can be shared between governments. Courts (perhaps the International Criminal Court) can be identified as possible locales for international crimes. A body of law can develop.
When it comes to nuclear weapons, one principle could be "inevitable disarmament." Nuclear weapons are too dangerous to have around any more. It might be just a matter of time before an accident flattens a major world power, or a trigger happy general decides a smaller-scale "tactical" weapon is worth using in the battle field. This would be an unmitigated disaster. Scholars can debate whether "mutually assured destruction" was appropriate during the Cold War, but in a multi-polar world where smaller states like Pakistan, Israel, Iran and North Korea all flirt with the technology, the risks go the other way. Instead, civilized countries should go back to thinking about how we can control, manage, and eventually get rid of the weapons.
When it comes to climate change, my favored principle would be "21st century leadership." There are significant, perhaps unparalleled, economic, political, and social benefits associated with implementing the infrastructure that can cut carbon and produce the new technologies for the 21st century. Countries like Germany are leading the way; meanwhile, the U.S. goes backwards, embracing 19th century technologies.
The real tragedy with not having any principle is that policies are made without any real thought, changing with the wind, unmoored from any strategy. The policy is dead on arrival, and usually with significant cost and/or body counts. It forecloses leadership based on ideas, and leads to a diminution in power, since a country can no longer lead with its ideals.
Time to get back to principle in foreign policy.