DW: You write in your book that civil war has become the most widespread, most destructive and most characteristic form of organized human violence. Can you briefly explain why?

David Armitage: Most widespread because there are almost no wars between states anymore as their number has been declining since the Second World War and probably the only conflict between two states that is going on is between India and Pakistan over Kashmir. The remaining 40 or so conflicts around the world are all internal conflicts or began as internal conflicts, and we know that the casualties that arise from these internal conflicts or civil wars have amounted since the Second World War to about half the number of people who died in the Second World War itself.

Economists have calculated that the price tag for civil wars every year amounts to somewhere in the same region as the development aid the Global North gives to the Global South. So civil wars collectively are incredibly destructive, and they could be seen now as the most characteristic form of human violence, because we don't engage in what used to be the most characteristic form of organized large scale human violence - war between states - much any longer. Those have declined for a variety of reasons, but civil wars have remained tenaciously with us.

Harvard history professor David Armitage

One of the most intractable civil wars with hundreds of thousands killed and millions displaced has been raging in Syria for six years now. Why have all efforts to stop it failed so far and what needs to be done to end the carnage?

In the Syrian case the signals are somewhat typical of contemporary civil wars, in that no ongoing civil war is entirely civil - in the sense of only being fought by members of a single community. The Syrian civil war is a classic example of what scholars call an internationalized civil war, which is a civil war that draws in outside parties and regional powers and that also draws in major powers from far away to fight their proxy wars. Russia is, of course, a very important example here. But the war has also drawn in a transnational terror organization like ISIS. The results of that civil war also spill massively over the borders of Syria itself - in the fate of the displaced persons and refugees who spilled out across the Mediterranean and Europe and West Asia.

All of this makes this a particular intractable problem: The proxy buy-in of major powers - Russia and the US in particular - the complexity of the regional overspill, and the sheer long-term damage which has been done to the Syrian state and the Syrian economy. For those reasons I think it is one of the most intractable conflicts for resolution, and it is very difficult to see at the moment how that can be resolved - except by at least beginning with multi-power agreements on a truce and then a peace deal followed by a massive effort of political reconstruction. But that is going to be of immense complexity, and it is therefore not at all surprising that no solution has been found to that conflict yet.

You write in your new book that "around the world democratic politics now looks ever more like civil war by other means" and mention the US as an example. How would you describe what's happening there right now - and do you see any danger that that could turn into something like a civil war?

I think I wrote that line during the course of the election campaign. I had of, course, no idea of what the US was going to look like in the aftermath of the new presidency. What I was worried about then - and what I am increasingly worry about now - is deep political polarization leading to first complete incomprehension among people on two highly divided sides, the rise of a language of violence and even incitement of violence. We saw that from now-President Trump during the election campaign. The calling of one's political opponents enemies, rather than simply legitimate opponents, also seems to be increasingly on the rise.

I think we are at a very, very delicate moment. My sense is that to prevent the slippage of the language of civil war into some actual violence, it is absolutely essential that civil disobedience remain nonviolent. And I think the means of preventing civil war at this very heightened and very polarized moment is the mobilization of civil society against policies which seem determined to create conflict both internationally and nationally here in the US at the moment.

But it is not just in the US that politics appears to have become much more polarized and bitter recently: Many European countries have experienced a similar trend. What's your outlook for Europe where France and Germany will hold key election later this year?

This is also a very worrying picture. I think this goes beyond the rise of populism and the rise of the nationalist right. I think this is a broader crisis in democratic politics more generally. If we think of politics as a whole as a means of managing differences over fundamental and opposed values up to, but not including, the invocation of violence, I think we are reaching the very outer limit of democratic politics as it has been developed over the last 200 years with this deep polarization - the frightening invocations of violence in the language that one finds in the French elections, for instance. But it has also been the case in post-Brexit Britain and during the Brexit debates as well.

There's a strong sense that what we have come to understand as the necessary alliance between liberalism and democracy is coming apart. We are seeing the emergence of what some people have called illiberal democracies now, and illiberal democracies lead in the direction of silencing the voices of those with whom authoritarian leaders do not agree.

If there is any possibility of a trans-national alliance among populist-nationalist leaders Putin, Trump and May to some extent, possibly Marine Le Pen - if she manages to surmount the ceiling that the Front National has tended to bump up against in French elections - than that presents a terrifying picture for the future of democracy as well as the whole practice of politics as we have developed it at least since the Second World War throughout Europe. So I think this is a moment for great vigilance and for no relaxation of that vigilance across Europe because of the potentially cascading effect of elections in France, Germany and also the Netherlands on top of what has already happened in the UK and the US.

David Armitage is professor and former chair of history at Harvard University. His new book, "Civil Wars: A History in Ideas," was published last week.