Sometimes what doesn’t happen counts most. In late September, President Dmitry Medvedev issued a decree banning the delivery of the S-300 air-defense system to Iran after Moscow had signed a contract for the system in 2007 worth $800 million.

The figure may be much higher — from $11 billion to $13 billion — since other weapons were covered by the presidential decree: “battle tanks, armored combat vehicles, large caliber artillery systems, combat aircraft, attack helicopters, warships, missiles or missiles systems as defined for the purpose of the United Nations Register of Conventional Arms,” to use the language of the recent UN resolution placing sanctions on Iran. Why are the Russians willing to incur such losses? Or to put it another way, what are they getting for that money?

The United States and Israel had always been strongly against the sale of the S-300s, which can destroy multiple aircraft and missiles at a range of 150 kilometers and at altitudes of up to 27 kilometers. If Israel wanted to take out Iranian nuclear facilities, it would have to be done before the S-300s were installed. A sale would have essentially started the countdown to an Israeli attack.

Russia wants better relations with Israel, including a $300 million deal to set up a joint-venture drone plant in Russia. But that might now fall through since Russia has refused to scrap its deal to sell supersonic naval cruise missiles to Israeli enemy Syria. At the same time, though, Syria does not pose an existential threat to Israel in the same sense that Iran does. What Israel may actually fear is that Syria will transfer the technology to Hezbollah, which used a similar weapon to attack an Israeli warship during the 2006 Lebanon war. Still, subsequent Israeli investigation of the incident concluded that human error was at fault; the warship’s defense system, under normal conditions, should have stopped the attack.

Iran’s defense minister, Brigadier General Ahmad Vahidi, said Russia’s decision to not sell the S-300s to Iran “lacks logic” because the weapons system is not banned under the UN resolution, which concerns only conventional weapons. Vahidi is correct in a narrow sense.

But there is a wider logic in Russia’s decision, although it is neither the logic of commerce nor that of an overly strict interpretation of the UN resolution. Russia has made a fundamental decision to throw its lot in with the West. Russia sees the West as a source of investment and know-how and an ally against ravenous China. Many Russians both in the power elite and the opposition see China as the adversary in the resource wars of the future. Russia, the only European country sharing a border with China, also has border disputes with Beijing. The eastern Russian territory is so sparsely populated that Chinese guest workers must be imported, an abhorrent vacuum.

The refusal to sell S-300s to Iran is Russia’s $800 million membership dues in the exclusive club of the West. The next decade will bring political, economic and even military rapprochement. Russia will enter the World Trade Organization and work more closely with NATO. Soon, the next time a Russian oligarch buys a major sports team like the New Jersey Nets, it will be accepted calmly.

This is a sea change. Prime Minister Vladimir Putin may be still at the helm, but one suspects that it is Medvedev who is increasingly plotting the course. But what matters most is the slow, sure swing of the ship in a westerly direction.