Russian President Vladimir Putin might have intervened in Syria promising to end the conflict there, but things on the ground are only going to get worse, and Putin’s drive to subvert Western interests will only increase.

Russia’s ominous military buildup in Syria represents the most significant projection of force beyond the territory of the former Soviet Union since the Cold War. In the past few days, Russia has initiated a series of airstrikes against Syrian regime opponents. It has begun operating advanced offensive hardware, including fixed wing Su-24, 25, and 27 fighter jets, attack helicopters, drone aircraft, main battle tanks, and SA-22 surface-to-air missile batteries from its new base in Latakia, which is in the backyard of Assad’s stronghold.

Although Russia uses the threat of the Islamic State (also called ISIS) as cover, the Russian campaign is in fact geared toward keeping the Bashar al-Assad regime in power in Syria, effectively closing the path toward negotiated resolution that had been opened by the Iran nuclear deal. Russia also intends to maintain a major forward operating base in the Middle East, which will allow it not only to play a role in determining the regime that follows, but also the ability to influence events in the region beyond the current conflict.

However, of greater concern in the immediate term, there is little guarantee that Russia won’t use its high-end military weaponry in other destabilizing ways, such as through sustained attacks on opposition fighters backed by the United States and the Gulf States. Indeed, Russia’s initial air attacks weren’t even aimed at ISIS strongholds, but were targeted at more moderate anti-Assad groups. And there are already questions about the Russian air force’s ability to operate in the same theater as British, French, Gulf, Turkish, and U.S. air operations without endangering allied aircraft and pilots, intentionally or unintentionally.

Indeed, Russia has been playing a dangerous cat-and-mouse game with allied planes and ships across Eurasia for many months now. Among other things, it has been both flying in the flight paths of Western commercial and military aircraft and using ships and submarines to intermittently sail into Western countries’ territorial waters. In addition, Russia has staged a series of large-scale military exercises just across the border of Poland and several Baltic states, and its intelligence service actually seized an Estonian agent during last year’s NATO Summit and held him for several days.

But this intervention in Syria is doubly ominous. Not only does it go far beyond Russia’s intervention in Ukraine in sheer operational terms, but it will also cause the Gulf States, led by Saudi Arabia, to massively up the ante in terms of their support of anti-Assad Sunni rebel groups in Syria. In short, this regional war—that is now verging on a minor World War, given all the outside powers now engaged in military operations there—will be substantially prolonged just when anticipation had grown over a diplomatic resolution to the conflict in the wake of the Iran nuclear qua peace deal.

Russia's President Vladimir Putin, Foreign Minister Sergei Lavrov, U.S. President Barack Obama, and U.S. Secretary of State John Kerry attend a meeting on the sidelines of the United Nations General Assembly in New York, September 28, 2015. Obama and Putin agreed on Monday to direct their militaries to hold talks to avoid conflict over potential operations in Syria, a U.S. official said. Mikhail Klimentyev / Reuters PERCEPTION, MISPERCEPTION, AND DETERRENCE

The United States and its Western allies should not have been caught so off-guard by Putin’s shrewd but destabilizing move. Since the Russia invasion and occupation of Eastern Ukraine, Putin has been poking and prodding the West, seeking ways in which a militarily and diplomatically resurgent Russia can subvert Western security interests and force Western capitals to deal with Russia again as a major world power with its own unique set of legitimate interests.

But this was not just a sin of omission. It is also a sin of commission. By not confronting Putin and Russia sufficiently over its illegal invasion and occupation of Ukraine, the United States and its Western allies effectively gave Putin a green light to project force in other geostrategic hot spots.

When Putin stared down the West and the West blinked, the West lost its credibility and, with it, its ability to deter further Russian bad behavior. Most Western security experts, focused on the conflict over Ukraine itself, ignored the wider strategic ramifications.

Inside the beltway, pundits argued against arming Ukraine because they believed that Putin would only up the ante. In fact, the United States should have upped the ante itself. More than likely, Putin would have backed down. After all, the use of force is about the only form of statecraft Putin respects. Russia effectively shrugs off anything short of it, or the credible threat of its use. Even the sanctions, which have cost the Russian economy dearly, have not deterred him.

The West did do a better job after the Ukraine invasion, deterring Russian incursions into other parts of Europe. The United States fairly rapidly provided security assurances to Poland and the rest of East–Central Europe, forcibly drawing a line against Russian incursions into these former Soviet satellites. But after Crimea was lost, the immense damage to the highest tenant of international law—non-violation of sovereign borders—was already done.

Russia has a stronger set of interests in Syria and in the Assad regime than the United States and its Western allies do. And believing that the West probably wouldn’t fight back, it felt free to intervene and begin launching strikes. And now the West has a significant new Russian forward operating base on its hands in a pivotal part of the world. The seeds of this buildup were sown when Putin deftly inserted himself into the Syria equation over two years ago when the United States, United Kingdom, and France failed to enforce their no-use-of-chemical-weapons red line. But it was the failure to force Putin’s hand over Ukraine that emboldened him to make this newfound far-reaching move.

Since the West is unlikely to intervene in the conflict directly, deterrence is even more vital for the United States to establish and maintain. It is both strategically effective and cost-effective, but it is difficult to establish and maintain, and quite simple to lose. In fact, deterrence matters more when a superpower is either unwilling or unable to intervene in a crisis where its interests are clearly at stake.

Building deterrence back up is an arduous process; it cannot occur in the absence of carefully but forthrightly checking an opponent’s moves (or potential moves) by a combination of calibrated repositioning of military forces, engaging in military exercises, or the actual use of military force. However, the most difficult part is doing this in the middle of a crisis or conflict, as what might be effective in peacetime could well be escalatory in wartime. Hence, deterrence is likely to remain lost for the remainder of this conflict. Afterward, or simultaneously in other regions, the United States and its Western allies will need to painstakingly work on rebuilding deterrence against nefarious Russian interventions.

The timing of Russia’s intervention could hardly be worse. The Iran deal was, contrary to conventional wisdom, already having a salutary effect on the Syrian conflict. Not only has Iran reigned in its leader of the Quds Force (the foreign arm of the Iranian Revolutionary Guard) and backed off from its support of the Houthis in Yemen, but in Syria, Iran has negotiated two ceasefires and spoken publicly about finding a diplomatic solution to the conflict. With Russian and Syrian encouragement, it may now tack in a more disturbing direction by supplying hundreds of Iranian troops.

The United States had done itself a great favor by successfully negotiating the Iran nuclear deal. But now it is watching an earlier misstep come back to bite it. Assad will not be going anywhere soon. Nor will the war in Syria be winding down. And with Russia’s trademark unpredictability, it will surely be choosing yet another place to subvert Western interests.