In brief, prospects for ongoing US foreign policy are not encouraging. The Donald's ineptitude is such that he is certain to defer to "the best generals" in matters of war and peace, and Hillary's stance in the 2008 primaries and as Secretary of State suggest that she will continue her ongoing attempts to prove she has enough "balls" to be "one of the boys." Bernie Sanders will probably have significant impact on the Democratic platform, but the relationship between a party's platform and what happens when that party wins an election has little if any bearing on what its candidate does when elected to office.
The "War on Terror"
Tr*mp vacillates between isolationism and carpet bombing (along with use of torture and killing the families of terrorists), but his commitment to building the size and strength of the military makes one wonder if "boots on the ground" might be inevitable — the military-industrial complex would like that, since it could restore sales to 2010 levels. Clinton has been largely silent on her suggestion of a "no-fly zone" in Syria lately, but her history on interventionism is troubling, including her vote for the war in Iraq and endorsement of intervention in Libya. Neither has any fresh ideas for dealing with the Islamist State as an international threat, even if Obama's efforts to cut into the territory it occupies continue to make progress.
The Middle East
It seems clear that Clinton will maintain US support for the Arab autocracies, despite copious human rights abuses within their territories and Saudi war crimes in Yemen. She also will be more friendly to Netanyahu's increasingly bellicose and repressive path for Israel than Obama has been, and the Palestinians will be out of luck, no matter what Bernie gets into the Democratic platform. Tr*mp's support from Sheldon Adelson suggests that he will be even deeper in Netanyahu's pocket than Clinton; and his rejection of the Iran deal and insistence that the Saudi's "pay their own way" would be a recipe for a nuclear armed Middle East. With regard to Assad, Tr*mp might be too conciliatory, Clinton too bellicose.
I don't know if anybody has considered problems that might arise from installing missile "defense" systems (against Iran? Yeah, right!) in Eastern European countries moving ever closer to fascism, but that probably can wait for 2020. Neither US candidate has anything to offer Europe in dealing with its refugee crisis, and neither will use US influence over the IMF in an attempt to soften Europe's devastating austerity regime, albeit neo-liberal (aka neo-conservative) US bankers have a lot more influence than US political leaders. Clinton certainly understands Europe's problems better than Tr*mp, but she's no less neo-liberal in her thinking than her husband was — and nobody knows what impact Tr*mp's affection for Putin might bring
Asia and the Pacific
The US Chamber of Commerce seems confident that Clinton will change her mind about support for the TPP as soon as she's president, and they're probably right. Tr*mp seems to think he could negotiate a "better deal," but his confidence in his negotiating skills is just as inflated as his hair. The Chinese, I suspect, couldn't care less which of them is elected because China's economic and military power is unlikely to be affected. Tr*mp's fantasies of Japan and South Korea having their own nuclear arms would almost certainly remain fantasies, because not all Republicans are total idiots.
If Tr*mp can identify more than three African countries on an outline map, I'd be very surprised. Clinton, at least, is aware of the mess that is African politics and economics, but is unlikely to move beyond Obama's very limited engagement there. With either of them, Africa will remain on the back burner until something explodes.
Haven't you had enough pessimism for one post? It's certainly been enough for me, so I'll pass over Latin America — where the US has had virtually no policy at all since "our" dictators were overthrown — and save it for another day. In the meanwhile, though, keep an eye on Venezuela, Brazil, Mexico, Peru, Argentina, Honduras, El Salvador, Guatamala, et al. Tr*mp's "wall" won't keep the chaos south of the border.