Is US monopoly on the use of soft power at an end?
The term soft power was coined by Harvard professor Joseph Nye in 1990.
He wanted to dispute "the then prevalent view that America was in decline".
Instead, Prof Nye saw a US that "was the strongest nation not only in military and economic power, but also in a third dimension, I called soft power".
He defined soft power as getting the outcome you want using persuasion rather than coercion - in contrast to hard power, the use of force or military action.
Although the idea of soft power has gained currency in the worlds of diplomacy and journalism, the concept has its critics.
Some have rejected it altogether, arguing that it is only hard, military power that counts on the international stage.
Historian Niall Ferguson has dismissed soft power as "non-traditional forces such as cultural and commercial goods", by which he means the influence of big brands like Coca Cola or Levi's.
These may be enjoyed by people who don't then love the US in return.
But Prof Nye argues that this fails to allow for context; soft power or hard power can only be effective in the right situation.
"Tanks are not a great military power resource in swamps or jungles."
The Marshall Plan is an example that fits Prof Nye's soft power theory.
Immediately after World War Two, US President Truman was reluctant to help fund reconstruction in Western Europe.
But by 1947, containing Communism had become America's foreign policy priority. The US put $13bn into war-ravaged Western Europe in less than four years, that's worth about $100bn today.
Spending money on building a strong, democratic Europe was seen as investing in a buffer against the power of the Soviet Union.
Nowadays, providing emergency relief and humanitarian assistance after a natural disaster might count as soft power.
A current example is the deployment by the US of more than 3,000 troops to Africa to help with the Ebola crisis.
Power of the cinema
Perhaps one of the most powerful examples of soft power in action is the US film business.
Hollywood may be reluctant to get too close to Washington: it was notably burned by the communist purges of the 50s under Senator Joseph McCarthy.
But the movies made on the west coast depict an American view of the world which can be powerfully attractive to others - as Iryna Orlova can testify.
I meet her in a homely church hall in East Hollywood, where she's rehearsing with the Balalaika Orchestra of LA.
During a break, we sit and chat about her childhood in Kiev.
Irina smiles as she remembers the American films she watched growing up in the Soviet Union.
As a child, Irina was enthralled by Spartacus and the Wizard of Oz and later, she saw ET and Disney films with her own daughter.
It was these American movies that contributed to her impression of the US as a happy, sunny, place.
Eventually, Iryna left Ukraine and brought her family to live in America.
The US military has long recognised the power of the cinema and has a Pentagon Film Liaison Unit based in Hollywood.
This provides facilities for film-makers to use military equipment and even real troops as extras if required.
However, access is subject to script approval.
Lt Col Steven Cole, deputy director of the unit, says its main concern is accuracy. But he concedes there are some storylines it simply won't co-operate with if they present the military in what it considers to be an unflattering or unrealistic light.
He says the primary aim is to help educate Americans on what their Army does.
But with global box-office takings at almost $36bn in 2013, he recognises there is a significant audience in the rest of the world too.
A new source of US soft power has come from the recent innovations in technology, many of which have emerged from Silicon Valley in California.
Millions of people want a smartphone or access to Google. Social media has given a voice to ordinary people and has been co-opted into fuelling revolutions and uprisings, even if the aims do not always chime with "American" values.
Facebook and Twitter are global brands with American origins, burnishing the country's reputation for creativity and transformation and possibly creating more space for free speech along the way.
Twitter insists that it is only a conduit for its users and not a tool of soft power or anything else.
But Luis Villa of Wikipedia thinks US soft power is integral to the internet: "It's sometimes difficult to disentangle the values of the internet and the values of the US, particularly, freedom of speech, but that does sometimes clash with how people think of speech in the rest of the world."
Soft power, via the internet or the cinema, is one way to persuade people that your values are universal values.
But the limits of soft power are also apparent everywhere.
If you look back across the period since the end of the Cold War, the US has actually deployed rather a lot of "hard power" around the world; two wars in Iraq, Bosnia, Kosovo and Afghanistan and the current airstrikes in Iraq and Syria, to name a few and not to mention the use of drones.
In all these cases, soft power wasn't enough to avert a conflict or military intervention.
Also, as Prof Nye concedes, soft power can only work when people are receptive to the messages it's peddling.
So the movies may help to spread a US vision of what a free, democratic life might look like, but only if the people watching, recognise the importance of those values to them.
It seems unlikely that the violent jihadists of Islamic State will be persuaded to abandon their anti-Western vision.
But despite its brutal hard power approach to spreading its ideology through war, IS isn't averse to also exploiting soft power tactics, like using social media to disseminate their uncompromising views.
In fact it may be that the distinction between "hard" and "soft" power may be morphing into a new concept put forward by Prof Nye, that of "smart power".
He points to the World War Two as an example: the enemy was defeated with hard power but then brought back into the fold with the creation of institutions and alliances (soft power) which have lasted until now.
A similar case is made by some in relation to IS in Iraq and Syria. Former US Assistant Secretary of State PJ Crowley argues that while military power can degrade IS, it can't defeat or destroy the ideology behind it.
He says that will take soft power - although once again, that raises the question of whether you can successfully deploy soft power against an ideology which actively rejects Western values and ideas.
There is another complicating factor, the US may still be the only superpower but there are now new, competing visions of what the world should look like.
The success of China's economy provokes both fear and admiration though China would like more of the latter.
The 2008 Beijing Olympics probably marked the beginning of the Chinese government's efforts to nurture a soft power message. Since then, things have stepped up.
There has been an expansion of Chinese Central Television, with the broadcaster producing English language programming from Washington and Nairobi.
The Education Ministry is funding more than 450 Confucius Institutes which aim to spread Chinese language and culture.
Their locations include some 90 universities in North America.
But this attempt at building soft power has gone awry.
Earlier this year, the American Association of University Professors wrote a report criticising the presence of Confucius Institutes on US campuses.
The academics argued the Institutes were an arm of the Chinese state, which worked to "advance a state agenda in the recruitment and control of academic staff, in the choice of curriculum, and in the restriction of debate".
Tibet, Taiwan, and Tiananmen are said to be among the subjects that aren't open for discussion in the Institutes.
And in recent weeks, two prominent US universities have suspended their affiliated Confucius Institutes, as concerns about them grow.
So for now, China's state funded soft power message, is treated with some suspicion and has nothing like the impact of the more grassroots US version.
China is still feared rather than admired by most of its Asian neighbours (not least because of its military or hard power capacity) but over time, who is to say that Beijing's economic success, regardless of its political system, won't win over global admirers?
So does soft power really matter? Governments seem to value it even though soft power alone won't prevent wars or silence your critics - although it may help to win support for your point of view.
For now, US soft power, remains pre-eminent, America continues to succeed in selling us its culture, its ability to innovate and its way of life.
But there are competing economic powers and competing ideologies, all demanding to be heard, all wanting to persuade you to see it their way.
Wielding soft power effectively is set to get more complicated.