Ever since the late Samuel Huntington predicted that international politics would be dominated by a "clash of civilisations", his theory, first outlined in 1993, has found some of its keenest adherents among militant Islamists. The terrorists who inflicted mass murder on Paris are part of a movement that sees Islam and the West as locked in inevitable, mortal combat.
Leading Western politicians, by contrast, have almost always rejected Professor Huntington's analysis. Even Mr George W. Bush said "there is no clash of civilisations". And everyday life in multicultural Western nations, most of which have large Muslim minorities, offers a daily refutation of the idea that different faiths and cultures cannot live and work together.
In the aftermath of the Paris attacks, that core idea needs to be reaffirmed. And yet a necessary restatement of liberal values should also not prevent a sober acknowledgment of some malign global trends. The fact is that hardline Islamism is on the rise - even in some countries, such as Turkey, Malaysia and Bangladesh, previously regarded as models of moderate Muslim societies. At the same time, the expression of anti-Muslim prejudice is entering the political mainstream in the United States, Europe and India.
Taken together, these developments are narrowing the space for those who want to push back against the narrative of a "clash of civilisations".
Terrorist attacks, such as those in Paris, promote tensions between Muslims and non-Muslims - as they are intended to. But there are also longer-term trends at work that are driving radicalisation. One of the most pernicious is the way in which the Gulf states, in particular Saudi Arabia, have used oil money to spread intolerant forms of Islam into the rest of the Muslim world.
The effects are now visible in South-east Asia, the Indian subcontinent, Africa and Europe. Malaysia has long been held up as an example of a successful and prosperous, multicultural nation with a Muslim-Malay majority and a large ethnic Chinese minority. But things are changing. Mr Bilahari Kausikan, a former head of the Foreign Ministry in neighbouring Singapore, notes a "significant and continuing narrowing of the political and social space for non-Muslims" in Malaysia. He adds: "Arab influences from the Middle East have for several decades steadily eroded the Malay variant of Islam... replacing it with a more austere and exclusive interpretation."
The corruption scandal that is currently undermining the government of Prime Minister Najib Razak has increased communal tensions, as the Malaysian government has fallen back on Muslim identity politics to rally support. One junior government minister even recently accused the opposition of being part of a global, Jewish conspiracy against Malaysia.
In Bangladesh, a Muslim country with a secular Constitution, radical Islamists have been responsible for murders of intellectuals, bloggers and publishers over the past year. There has also been a rise in attacks on Christians, Hindus and Shi'ite Muslims. Much of this violence has been perpetrated by the Islamic State in Iraq and Syria or Al-Qaeda. But, as in Malaysia, the rise of radical Islam seems to have been heavily influenced by the Gulf states - through the funding of education and the connections forged by migrant workers.
Terrorist attacks, such as those in Paris, promote tensions between Muslims and non-Muslims - as they are intended to. But there are also longer-term trends at work that are driving radicalisation.
One of the most pernicious is the way in which the Gulf states, in particular Saudi Arabia, have used oil money to spread intolerant forms of Islam into the rest of the Muslim world.
For many in the West, Turkey has long been the best example of a majority-Muslim country that is also a successful secular democracy. But in the era of President Recep Tayyip Erdogan, religion has become much more central to the country's politics and identity.
Mr Erdogan has been labelled as "mildly Islamist" by The Economist and others. But there was nothing mild about his statement last year that Westerners "look like friends, but they want us dead; they like seeing our children die".
While Indian Prime Minister Narendra Modi has not said anything this inflammatory about Muslims, he has long been accused of tolerating anti-Islamic prejudice and violence. During his first months in office, Mr Modi reassured some critics by concentrating on economic reform. But in recent months, members of his Hindu-nationalist Bharatiya Janata Party have ramped up anti-secular and anti-Muslim rhetoric - with the lynching of a Muslim man, accused of eating beef, making national headlines.
In Europe, even before the Paris attacks, the migrant crisis had helped to fuel the rise of anti-Muslim parties and social movements. As Germany has opened its doors to refugees from the Middle East, violent attacks on migrant hostels have risen.
In France, it is widely expected that the far-right National Front will make significant gains in next month's regional elections.
Anti-Muslim rhetoric is also rising in the US and has become commonplace among Republican candidates for the presidency. Mr Ben Carson, who leads in many Republican polls, has said that no Muslim should be allowed to become US president, while Mr Donald Trump has said that he would deport any Syrian refugees admitted to the US.
The confluence of these developments in North America, Europe, the Middle East and Asia is fuelling the idea of a clash of civilisations. Yet the reality is that the Muslim and non-Muslim worlds are intermingled across the globe. Multiculturalism is not a naive liberal aspiration - it is the reality of the modern world and it has to be made to work. The only alternative is more violence, death and grief.
THE FINANCIAL TIMES