As a German, I'm not particularly impressed by the 'threat' that countries like Iran (which didn't invade another country for centuries) pose to world peace. Even if they were, I wouldn't be much concerned because they get a lot of attention already.
It's more likely that some threat that doesn't get the attention as such is a greater risk.
This includes especially aggressive allies.
The most interesting (potential) troublemakers are therefore in my opinion the U.S., Russia, UK and Israel.
We are formally allied with two, friendly with one and in practical relations (business-like) with another.
The UK seems to be rather disenchanted with military adventures and limited in its potential, while Israel is a strictly regional troublemaker. Russia is in a phase of stagnation if not steady decline. This leaves the U.S. as most interesting potential troublemaker.
Considering the scale of activity and the ease with which I can assess sources, I've made a habit of tracking developments in U.S. politics. In part for the entertainment value and in part because I am curious about which shitty foreign policy may come next and endanger my country (in)directly.
During the last two decades, U.S. foreign policies have indirectly led to several dozen dead or abducted Germans, while Russians, Israelis and British added pretty much none. The attention seems justified for a German MilBlogger.
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Now to my analysis of U.S. politics:
The political forces of conservatism and progressivism have their rightful places in a society, for neither is flawless enough to rule a sustainable society.
The conservative political forces in the U.S. are ill-represented by the Republican party and its progressive political forces are ill-represented by the Democratic party. It's a textbook version of a simple majority rule political economics.
The fundamental divide between both parties is about the question of government-organised solidarity. Democrats want the government to support unlucky citizens institutionally (social safety net) and Republicans largely reject the same. There are more conflict points, in which the Democrats typically assume the more secular position.
This lack of consensus on the fundamental nature of government is quite typical, for the U.S. has still no consensus on topics where Germans have reached (and maintained) a consensus (with overwhelming and robust majority in favour of one option) sometime between the 1880's and the 2000's: Evolution, social insurances, secularism, the age of earth, global warming, imperial foreign policy, torture, Pigou taxes...
The current political conflicts of the U.S. are (luckily) mostly of domestic nature and seem to pose no martial threat to other nations, albeit an economic threat seems to persist.
The Republicans have a simple grand strategy; they do whatever they feel they want to do when they are ruling and they attempt to defund the Democrats' attempts to realise democratic policies whenever Democrats occupy the White House.
This explains why the traditionally pro-budget deficit Republicans now fake to be the fiscal austerity party. It's all about defunding Democratic policies.
The Republican leaders in Congress do not have the outer appearance of being tough guys (a charisma-free double chin and an orange-faced guy who often cries in public), but their tactics are very tough.
A normal political compromise is a give-and-take thing. Their idea of a compromise is to take and to promise not to take even more (by defunding) - at least for a while. This partially explains Republican extremism; it generates free bargaining chips for foul political compromises. (From a German point of view, left-wing extremism in the U.S. only earns the "extreme" rating by the fact that the right wing moved so far away from it.)
This strange idea of what constitutes a compromise extended into Republican foreign policy for the last two decades and explains much of it - especially its inability to come to a cooperative conclusion in many conflicts.
The democrats are meanwhile a faint version of social democrats, persistently disadvantaged by the fact that their political program requires funding. Their political strategies lack the Republican aggressiveness, especially the preventive aggressiveness as displayed by the Republican idea of a bipartisan compromise.
Both parties are nevertheless quite exchangeable in regard to a long list of assumptions, myths, prejudices and in their pro-big business stance. Neither is able to sustain political ideologies that run counter to powerful business lobbies.
There are thus many constants in U.S. foreign policy. The methods vary, but the beliefs are largely the same.
It's therefore not possible to tell whether a Democratic or a Republican president is more of a threat to foreign countries.
There is also an advantage in this stability; the behemoth USA is unlikely to turn on Allies or (perceived) threats suddenly and without obvious early indicators. The move against Iraq was prepared in and out of government for a decade and the more general conflict with Arab terrorists was even obvious in pop culture (C-movies) for almost as long. The U.S. portrays its targets as villains long before it strikes. This is sometimes accompanied by a scare campaign; red scare, yellow scare, Muslim scare, terror scare ...
Right now, there are some early indicators for a conflict with the PR China, but this has likely to become a broader movement before the country is ripe for open conflict. Preparing the grounds for open conflict on a more popular base will likely take another 4 to 10 years. Watch out for Hollywood villains of Chinese origin not played by Jet Li.
There have also been many early indicators for a decoupling from Europe; widespread French-bashing, "Old Europe" criticism, popular derogatory remarks on different European nationalities and the myth of a Muslim invasion or take-over of Europe are concerning.
A complete decoupling may of course create the option of open conflict between European powers and the U.S., something that hasn't extended beyond minor trade wars for generations.
A reverse of this with public diplomacy and cultural influence might help to prevent open inter-Atlantic conflict in a generation or two.
A growing population share of so-called "Hispanics" (emigrants from Latin America, many of them would be considered by Europeans to be whites) and a slight increase of relations to and cultural influence from India might be very, very early indicators for increased affinity to Latin America and India.
It may be true that the behemoth USA is astonishingly easy to manipulate with money. Lobbyism and funding of manipulative popular entertainment. Entertainment programs that fake to be news programs or fake to only fake to be news programs are such an example. Powerful lobbying businesses are ready for service to customers as well, complete with fake grass-roots movement (so-called 'astroturf' projects) and revolving door between politics and lobbyism.
There's little reason to believe that China would be more challenged to influence U.S. foreign policy than Israel, for example. You probably don't need to do much more than some lobbying, buy some shares in TV and radio stations, meet important people and finance some Hollywood movies with a suitable narrative.
Overall, Germans are not threatened by the U.S. directly (save for a huge deal of espionage and occasional abduction), but we should pay attention to staying out of a possible Sino-American open conflict and we should perceive NATO as the bond that prevents open rivalry if not open conflict between the U.S. and Continental Europe.