BRUSSELS ― Russia’s seizure of Crimea is the most naked example of peacetime aggression that Europe has witnessed since Nazi Germany invaded the Sudetenland in 1938. It may be fashionable to belittle the “lessons of Munich,” when Neville Chamberlain and Edouard Daladier appeased Hitler, deferring to his claims on Czechoslovakia. But if the West acquiesces to Crimea’s annexation ― the second time Russian President Vladimir Putin has stolen territory from a sovereign state, following Russia’s seizure of Georgia’s Abkhazia and South Ossetia regions in 2008 ― today’s democratic leaders will surely regret their inaction.

In Western capitals, the response so far has been mixed. The punishments being considered ― expulsion from the G8, for example ― would be laughable were the threat to Europe’s peace not so grave. Putin regards the breakup of the Soviet Union as the greatest catastrophe of modern times, and he has sought relentlessly to refashion Russia’s lost empire. If the West intends to be taken seriously, it needs to act as decisively as Putin has.

Putin’s many successes in his imperial project have come virtually without cost. His Eurasian Economic Community has corralled energy-rich states like Kazakhstan, Uzbekistan, and Turkmenistan into Russia’s camp. Georgia was dismembered in 2008. Armenia’s government was bullied into spurning the European Union’s offer of an Association Agreement.

Now the greatest geostrategic prize of all ― Ukraine ― may fall into Putin’s hands. Russia without Ukraine, former U.S. National Security Adviser Zbigniew Brzezinski wrote, “ceases to be an empire, but Russia with Ukraine suborned and then subordinated, Russia automatically becomes an empire.” And, because the vast majority of Ukrainians have no desire to join Putin’s empire, we can be certain that the state Putin will lead from this point on will be a highly militarized one, rather like the Soviet Union but without the ruling Communist Party.

Given the scale of Putin’s adventurism, the world’s response must be commensurate. Canceled summits, trade deals, or membership in diplomatic talking shops like the G8 are not enough. Only actions that impose tangible economic sanctions that affect Russian citizens ― who, after all, have voted Putin into power time and again ― offer any hope of steering the Kremlin away from its expansionist course.

Which sanctions might work? First, Turkey should close the Dardanelles to Russian shipping, as it did after the 2008 Russo-Georgian War. Back then, Turkey closed access to the Black Sea to prevent the U.S. from intervening, though the U.S., it is now clear, had no intention of doing so. Today, it should close the Turkish straits not only to Russian warships, but to all commercial vessels bound for Russia’s Black Sea ports. The impact on Russia’s economy ― and on Putin’s military pretensions ― would be considerable.

Turkey is permitted to close the Dardanelles under a 1982 amendment to the 1936 Montreux Convention. Indeed, Turkey could turn Putin’s justification for seizing Crimea ― that he is protecting ethnic Russians there ― against him, by arguing that it is protecting its Turkic Tatar kin, who, given Russia’s ill treatment of them in the past, are anxious to remain under Ukrainian rule.

Turkish Foreign Minister Ahmet Davutoglu turned his plane around in mid-air this week to fly to Kyiv to offer support to the new interim government. Prime Minister Recep Tayyip Erdogan, no pushover himself, as Putin well knows, should follow up on that gesture of support by immediately closing the straits to Russian shipping ― until Putin recalls all troops in Crimea to their Sevastopol bases or to Russia proper. And Turkey should be offered an Article 5 guarantee from NATO should Russia seek to intimidate it.

Second, U.S. President Barack Obama should impose the type of financial sanctions on Russia that he has imposed on Iran for its nuclear program. Those sanctions have crippled Iran’s economy. Similarly, denying any bank that does business with a Russian bank or company access to the U.S. financial system would create the kind of economic chaos last seen in Russia immediately after the fall of Communism. Ordinary Russians should be made to understand that permitting Putin ― whose primary claim to leadership is that he ended the penury of the first post-Soviet years ― to continue with his imperialist aggression will cost them dearly.

Third, Obama should emphasize to the Chinese their stake in Eurasian stability. Putin may regard the Soviet Union’s disintegration as a tragedy, but for China it was the greatest geostrategic gift imaginable. At a stroke, the empire that stole millions of hectares of Chinese territory over the centuries, and that threatened the People’s Republic with nuclear annihilation, simply vanished.

Since then, Central Asia’s independent states, and even Ukraine, have become important trading partners for China. Russia’s conquests in Georgia greatly displeased China, as was seen at the post-war summit of the Shanghai Cooperation Organization (a regional grouping that includes ex-Soviet countries that share borders with China and Russia). Russia pushed the SCO to recognize the independence of Abkhazia and South Ossetia. But the SCO balked. The group’s Central Asian members ― Kazakhstan, Kyrgyzstan, Tajikistan, and Uzbekistan ― would not have stood up to the Kremlin without China’s support.

Today, however, Chinese President Xi Jinping may need to be less cryptic in his response to Putin’s adventurism. Indeed, the real test of China’s claim that it is a responsible stakeholder in the world community will come soon at the United Nations. Will it back Putin’s clear flouting of international law, or will it back Ukraine’s territorial integrity?

There are other possible punitive measures. Visas can be denied and canceled for all Russian officials. Assets can be frozen, particularly those laundered by oligarchs close to Putin. Only when the pain becomes intolerable, particularly for the elite, will Putin’s kampf be defeated.

The cost of inaction is high. Countless countries, from Japan to Israel, rely on America’s commitment to act robustly against grave breaches of the peace. Moreover, when Ukraine surrendered its nuclear weapons in 1994, it did so with the express understanding that the U.S. (and the United Kingdom, France, and Russia) would guarantee its territorial integrity. Should Crimea be annexed, no one should gainsay Ukraine if it rapidly re-nuclearized its defense (which it retains the technological capacity to do).

When Chamberlain returned from Munich, Winston Churchill said, “You were given the choice between war and dishonor. You chose dishonor and you will have war.” Obama and other Western leaders face a similar choice. And if they choose dishonor, one can be certain that an undeterred Putin will eventually give them more war.

By Charles Tannock

Charles Tannock is a member of the foreign affairs committee of the European Parliament. ― Ed.

(Project Syndicate)