I generally avoid unfalsifiable generalizations about historical epochs, but in this case I will indulge myself. I believe that Russia’s occupation and annexation of Crimea is going to prove as much of an inflection point in post-Cold War history as the terrorist attacks of September 11, 2001.

Roughly speaking, the period between the dissolution of the Soviet Union in December 1991 and September 11, 2001 can be thought of as the era of liberal-democratic ascendancy – that is, it was a period when Francis Fukuyama’s “end of history” argument about the absence of significant ideological challengers to liberal democracy on the world stage was more-or-less correct.

That era ended on September 11 when it was made very clear that political Islamism had become a potent mobilizer of militant opposition to the ideological hegemony of liberal democracy. What followed was the era of “The Global War on Terror,” during which the United States, and most of the world’s other major powers, were preoccupied, to one degree or another, with security challenges from militant Islamist movements.

We have now entered a new era in which great power contestation is once again replacing “terrorism” and asymmetrical warfare as the principal threat to international order. The new era is going to be dominated by an old-fashioned – as well as unstable and dangerous – struggle for influence among three, and possibly more, poles of state power – the United States and its key liberal-democratic allies, Russia, and China.

In making this claim, I don’t mean to suggest that terrorism as a political instrument or militant political Islamism as a mobilizer of violence is passing into history. They are not. Indeed, jihadists have every reason to believe that their international struggle is more successful now than ever, with fronts opening up from South Asia through the Middle East and Africa – and above all in Syria and Iraq, as highlighted by the assault on Mosul this past week. But non-state actors cannot deploy violence with anywhere near the efficacy of states. If at some point it becomes easier for non-state actors to get their hands on weapons of mass destruction, we will enter into an even more volatile and dangerous era. But for now states remain by the far the most capable actors when it comes to violence.

Fortunately, the risk of war between great powers is modest, and hopefully it will remain so, above all because the costs of interstate war today can be so enormous. But they are not insignificant, and they have gone up significantly in the wake of Crimea’s annexation. It is the potential costs of great power conflict, and the costs of trying to avoid interstate war through deterrence and agreed upon rules of the game that make managing great power politics so daunting. They are also why great power relations are going to be much more central security concerns for Washington and its allies than they have been since the collapse of the Soviet Union.

The increasing salience of great power contestation was evident well before Crimea’s annexation (just as the power of political Islamism to mobilize violence was evident well before September 11). But what Crimea has done is highlight the centrality of the contest as well as its dangers. For the first time in post-World War II history, an internationally recognized state with a seat in the U.N. General Assembly – and, more importantly, one with a permanent seat on the Security Council – occupied and annexed part of the territory of another state with internationally recognized borders and a seat in the General Assembly. In annexing Crimea, Russia also brazenly violated a host of international commitments – including, but not only, the United Nation’s Charter, the Helsinki Final Act, the 1994 Budapest Memorandum, its1997 Treaty of Friendship, Cooperation, and Partnership with Ukraine, and its 1997 and 2010 basing agreements with Kyiv for the Black Sea Fleet. In doing so, it was signaling that old rules of the game governing great power relations no longer applied. At the same time, it has undermined the constraining force of existing agreements with Russia, including arms control agreements, and it will make entering into new international agreements with Moscow much more difficult politically for Western countries in particular.

One of the implications of all this is that for the foreseeable future the states that border on Russia cannot assume that the Kremlin will respect their territorial integrity. On the contrary, not only those countries with strained relations with Moscow but its putative allies – notably Belarus and Kazakhstan – will have to assume that Moscow may decide to openly violate their sovereign territory in pursuit of its geopolitical interests. And with Crimea as a precedent, China’s neighbors in East, Southeast, Central, and South Asia are likewise going to assume that China, too, is now more likely to use force to back up its territorial claims and in pursuit of its geopolitical objectives.

Russia and China will thus be “revisionist” powers in this new era. The leadership in both countries is convinced that the current system of international institutions, norms, and alliances does not serve their interests well, is not particularly just, and does not reflect the evolving balance of power in their respective regions. Both will continue to try to change those institutions, norms, and alliances, and both will continue to take steps to divide the West and undermine its power and influence, particularly but not only in areas that they consider to be rightfully within their sphere of influence. And at least initially, Russia and China are going to cooperate – albeit warily – in challenging America’s claim to “world leadership.”

As a result, the relatively brief period when U.S. security officials could assume that the principal threats to national security came from non-state sources and transnational problems (transnational terrorism, “failed states,” water scarcity, organized crime, etc.) is over. While states have new weapons of war at their disposal (particularly in cyber-warfare), the nature of the contest is going to look pretty old fashioned – alliances, balancing and counter-balancing, soft power, and propaganda, but also instruments of hard power – combat aircraft, ships, and tanks.

In sum, I believe the international environment is getting much more dangerous for the United States and its allies very quickly. What is going to make this new era particularly dangerous is precisely the absence of agreed upon rules of the game along with the contested boundaries of old-fashioned spheres of influence. Moreover, I think that the American public is unaware that what the Soviets used to call the “correlation of forces” is headed in the wrong direction – indeed my principal beef with President Obama on foreign policy is that he has failed to use the bully pulpit effectively to warn the country that its overseas challenges are getting worse, not better. And he has failed to convey with sufficient clarity that U.S. power is being strained by the simultaneous challenges of an increasingly assertive (and indeed aggressive) Russia and China, along with a resurgent jihadi movement.

With Russia, we are moving into a dangerous period of an inevitable, and in my view appropriate as long as it is carefully calibrated, Western military response to the Ukraine crisis. The political struggle over the nature of that response, and Russia’s reaction to it, are likely to come to a head at the NATO summit in Wales this September, a topic I will address in my next post.