In the wake of the change in status in Cuba, the nuclear deal with Iran, and various political figures inveighing about China or Russia, I felt it might be useful to offer something like a primer on diplomatic relations.
1) "We only make peace with our enemies, that's why they call it making peace". - You generally don't have to ask your friends for stuff. They know you well enough to know what you might like, what you might need, and if they have it, sometimes they just give you something to keep you happy (in part in the expectation that you would do the same). But for people that you don't know, we usually have to give them money, or bargain or talk or otherwise arrange to get what we want. Over time, if you do this a lot, other people come to know and trust you and might offer things in a more casual way. The ideal position is to make them not hostile and friendly or receptive to your interests and agenda. There are many avenues to that point.
Rule: Diplomacy isn't as necessary with your allies and client states as a hegemonic power like the US. It is needed with your rivals or states you see as hostile to your interests and agenda.
2) By far the cheapest way to get what you want is to talk for it. Followed by bribing for it. Bombing people, as with beating people up, is not cheap and costless as it is often portrayed as "just another option". Lives are lost, people are angered and thrown into grief and despair, economies are mangled by all the destroyed infrastructure, homes are destroyed, placing thousands, if not millions, as potential refugees fleeing the violence rather than trying to rebuild. There are a lot of consequences. If you throw money into it and don't get what you wanted, all you have lost is money. Trade is also not the same as throwing money away. Even a trade deficit or outsourced labour is a potential avenue for diplomatic and human rights/economic advancement for both countries involved. If you throw talk at someone and get nothing useful in return all you have lost is time. Both time and money are valuable, but taking or losing lives is more expensive than both (it also costs both).
Rule here: Don't take lives or risk lives if you don't have to to get what you want.
3) If you talk and don't get what you want, try listening as well. Sometimes there is a deal there to be made if you pay attention to what the "other guy wants". There seems to be an assumption that asserting loudly what you want is the way to get it. I'm not aware of this working on an individual level usually. Maybe sometimes. It is not generally how international relations functions. Telling people off for not doing what you want tends to assure they won't do it. Maybe if they really want to avoid a war.
Basic rule: other countries have legitimate interests and needs for their country and populace to prosper. Being more aware of these may make it easier to achieve your own interests.
4) Belligerent talk is also ill-advised as it has to be backed up once in a while or you're just a loud-mouthed bully. It commits you to a course of action rather than retains it as a course of action. This also assumes that a war will gain you want you want. In the cases of Russia and China, both countries are nuclear armed. War could be very, very costly indeed. In the case of Iran, it's very unclear if a war would gain us what we want (which seems to be a regime change in the case of hawks). I would say that it seems to me that the Green revolution was overblown as a source of political change and upheaval in Iran, just as various Russian orbit countries (like Ukraine or Georgia) experienced modestly democratic revolts in the breakup of the Soviet Union but little that should give us confidence that these are "reformed" nations (the Baltics may be a different case).
In the past 25 years, the only intervention of a sort I can think of that has "ended" positively thus far might be Serbia, and the intervention there that worked had more to do with the ICC than our bombing campaigns. Somalia, Kosovo, Haiti, Rwanda, Bosnia, Iraq (twice), Libya, Yemen, Colombia, Honduras, Afghanistan, Pakistan. None of these should be global locations that inspire confidence in the ability of the American military to establish or re-establish a peaceful and prosperous people in some other country or territory far afield. I don't think that's what it is for generally speaking. Too often even American diplomats think it is (see: Albright).
Bombing Iran weakens any internal opposition to the regime, not strengthens it. Talking about China's misdeeds on human rights in an overt and hostile/belligerent way via our diplomatic channels or our Presidential bully pulpit risks committing us to a longer-term strategy of rivalry and opposition. The current longer term strategy of trade and diplomacy does not, even if currently frustrates some number of people who harbor a degree of anti-China bias (it also opens us up to some similar charges, given the record of torture and imprisonment we have accumulated over the last decade plus and have not dealt with yet). Pushing the countries surrounding Russia into a pro-Western orbit of protection both prevents this from happening naturally and adds to the isolation and paranoia of Russian views that they are being threatened, increasing rather than decreasing the likelihood of events like those in Ukraine (or Georgia, though there much more was done by Georgia itself on the theory that it was already supposedly within this orbit of protection).
Takeaway: Remember that war is very costly and its gains, if any, are often uncertain and will be exaggerated by more hawkish forces within a country while costs are minimized or ignored.
5) All this talking and wheeling and dealing does not mean you don't keep an eye on your rivals to be wary of things they might do that are belligerent, hostile, or undesired. That's why we have a military and various intelligence agencies and intelligence gathering options. As unpleasant as it may be to talk to unsavory people and give them things, none of this means we cannot take it away. What it means is we reserve our ability to strike and gather information for the things we actually have to take away instead of mindlessly bombing everything that we "could" take away on the theory that this would help. Our goals for decisive, military interventions should remain very clear, very achieveable, and often with the understanding that military power is limited. Soft power is limited in some respects too, but in the manner that we often talk about the uses of military power (regime changes for instance), I would place more trust on diplomacy and trade and espionage getting us what we want and keeping things in check than repeated bombing campaigns.
6) It's much easier to amass soft power or to use military power when you have assembled allies. And those allies also have interests or limits on what they are willing or able to do with or for you. If our allies want or believe a deal with Iran or trade with Cuba is more sensible than our proposed alternatives, even if we believe they are wrong, it is generally smarter to go along with them than to try to enforce something by acting alone, particularly if it doesn't seem to matter very much to us. Only if something is essential to national interest and security does it matter to enforce it over objections. This was not the case with Cuba and the embargo, or the case with Iran. Or at least, not having a deal with some degree of intrusive monitoring of their nuclear program was not preferable to having such a deal if the goal is to reduce the likelihood of Iranian nuclear weapons. More to the point, the threat of an Iranian nuclear weapon is at this point fairly minimal. Pakistani nuclear weapons represent more of a threat for international terrorism or world peace. Or Russia's still massive arsenal. Or even North Korea. All of these countries have had these arsenals for years, if not decades, without a serious incident (Cuban Missile Crisis and Able Archer 83 to the contrary). It is unclear how this arithmetic changes with Iran.