It's not often that an American election sparks debate about a philosopher. But ever since Mitt Romney announced his selection of Paul Ryan as his vice presidential candidate, talk has turned to the ideas of novelist-philosopher Ayn Rand.

Ryan is on record as being a fan of Rand's, and although he has taken pains to distance himself from her entire philosophy, he continues to stress that her novel Atlas Shrugged "is a great novel". Ryan is far from the only one who thinks so. Since the financial meltdown of 2008, Rand's 1957 novel has sold more than 1.5 million copies.

But here's something interesting: virtually all of those sales took place in the US. Why are so many Americans, from students to politicians, talking about Rand's novel — and why are her books comparatively unknown in Europe?

The answer to both questions is the same: Atlas Shrugged is a hymn to the American spirit.

The American spirit is characterized by independence, individualism, political and economic freedom, and productive ambition. It's the sense of life best summed up in the American Revolutionary motto "Don't tread on Me." It was this spirit that led so many Americans to rebel against the post 2008 expansion of state power. They didn't just see big government as a threat to the economy: it was an affront to their whole conception of what America is about. After eight years of Bush and eight minutes of Obama, they were fed up with being tread upon.

Atlas speaks to this spirit. Set in a world eerily similar to ours — a world where the economy is crumbling, where government intervention is growing, and where productive individuals are denounced and drained for the sake of the unproductive — it tells the story of men and women who decide to stop being tread upon.

But the dramatic story contains a powerful intellectual punch: Atlas gives the American spirit a philosophic defense it has never had. The American spirit often has been attacked as atomistic, cruel, and materialistic. Atlas blasts any such notion. It shows that capitalism is a win-win system where all individuals are free to pursue their happiness. It shows that it is right for individuals to be concerned with their own happiness. And it shows that those who seek to "tread on you" — to control your life, redistribute your wealth, and mortgage your future — are morally wrong

It's no accident, then, that Ayn Rand's immense popularity in America has not crossed over to Europe. It's for the same reason that Europeans largely embraced the government's post-financial crisis interventionist policies — from bailouts to stimulus spending sprees to vast new regulatory powers — while Americans rebelled. Whatever motto best captures the European attitude toward life, "Don't tread on me" is not it.

Ayn Rand wrote Atlas, in part, as a warning to Americans. She believed that, as early as 1890, America had veered from its free-market roots and was descending into statism. (She would have regarded as absurd the widely-held notion that America in the years before the financial crisis had anything resembling a free market.) To reverse that trend, Americans would have to translate their individualistic spirit into an explicit ideological program: one that upheld individualism and laissez-faire capitalism as moral and political ideals.

To succeed in this task, Rand argued, Americans would need to question and reject the alien idea of altruism. Altruism is the Old World doctrine that it's your duty to live for others and renounce your own self-interest. In one form or another, this moral doctrine has been the justification for every welfare program. Other people need money for their retirement or healthcare, it's claimed, and therefore they're entitled to that money from you. The individual's pursuit of his own happiness versus altruism — this is the choice facing America.

Although Rand was primarily speaking to Americans, she was not only speaking to Americans. The spirit of America, she held, is open to any individual willing to think. Today, as Europe is doubling down on the welfare state, that spirit, and the ideas of Atlas Shrugged, are needed more than ever.