China's rapid economic growth in recent years has changed the global balance of financial power. That's a challenge to western nations. But China's subsequent drive toward military ascendancy may be an even bigger challenge.Historically, China hasn't been one of the world's military big boys. The Chinese have been pushed around a lot over the years, most notably by Britain, Japan and the United States. That isn't likely to continue as China develops. Middleweights can put on a lot of muscle in a hurry when they have money, determination and technical skills. China has all three in spades.The world's most recent power studs have been the United States and Russia. For decades they have had the potential to blow each other and their neighbours to bits. That was frightening, but eventually this ultimate terror led to enough negotiated agreements between the two countries to produce some degree of calm on the nuclear front.Overall the balance of power tilted very much America's way. On the high seas, in particular, the Americans dominated, having long ago replaced Britain as hall monitor. The Americans' ten massive aircraft carrier battle groups have cruised the world's waters, instilling fear in would-be disrupters of international order. Each of these carrier groups has been loaded with more firepower than most nations' armies, navies and air forces combined.Again, these flotillas have engendered a degree of calm – at least for America's allies. Yes, they can scare the wits out of any bothersome government they turn their sites on. But their very presence has pre-empted the escalation of combat in a variety of international trouble spots.I have twice had the opportunity to sail on American aircraft carriers and have been struck by their boundless weaponry, including carriers, their waves of aircraft, guided missile cruisers, destroyers, frigates, submarines . . . a collection stunningly organized and intimidating.Enter the Chinese.Toward the end of the 20th century the Chinese government woke up to the fact that having all kinds of American firepower moving at will on its littoral waters was not conducive to its intention of enforcing its territorial claims in disputes with neighbours, including Japan and Vietnam.As a result China has quietly developed the world's first land-based missile system – Dong Feng 21Ds – capable of sinking aircraft carriers from a long way off: to wit, more than 1,500 kilometers, or a bit more than the distance between Winnipeg and Vancouver.That's a long way out into the East and South China Seas – farther, for instance, than the range of U.S. fighter jets that might try to take the missiles out before they are fired. This would be no mean feat at any rate, given that they have mobile launchers and China has developed an elaborate series of hardened underground tunnels. (The Chinese are also advancing hypersonic glide vehicle technology that would allow missiles to change course as ships attempt to dodge their approach).The DF-21Ds feature multiple warheads that can carry conventional or nuclear weapons. They are capable of getting to their faraway targets in about 12 minutes. The Americans are known to be working with fierce determination on coming up with ways to defend against them. They may already have devised ways of deflecting them, evading them, or in some other way avoiding them. Or not.If not, the Chinese have clusters of $10 million weapons capable of taking out aircraft carriers worth between $3 billion and $4 billion apiece. Those kinds of exchanges would be a real bargain for the Chinese.The very existence of these missiles has shifted the balance of power in waters that President Obama – in his announced “pivot to the Pacific” – has recognized will be the main theatre for naval warfare in the coming century. That is disturbing enough. But what is even more disturbing are the implications for the big picture: the balance of nuclear deterrence that the United States and the Soviet Union and its Russian successors have so carefully put in place.The development and testing of the DF-21D would not have been allowed under the Intermediate-Range Nuclear Forces Treaty (INF) signed by U.S. President Ronald Reagan and Soviet General Secretary Mikhail Gorbachev in 1987. But China – a military pipsqueak in those days – is not a signatory to that treaty. Neither is India, which is developing its own missile technologies.The Soviets and Americans – even before the end of the Cold War – recognized that ballistic and cruise missiles (either nuclear or conventional) with ranges of between 500 and 5,500 kilometers were a major threat to either country's capacity to defend itself, and incompatible with any workable system of international arms control. So they agreed to cease developing them, and destroyed those that had already been built.The Chinese government wasn't fettered by any international agreement when it decided that it would design potent missiles capable of flushing American warships out of its littoral waters.The United States should hold a commanding military edge over China for the foreseeable future. As much as the Chinese have expanded their defence budget to about $200 billion a year, it is still only about a third the size of the U.S. budget. But the DF-21D fits in with China's overall development of a new generation of missiles – both submarine-launched and intercontinental – designed to bolster its capability to overwhelm U.S. missile defence systems. The DF-21D – if it works as advertised – is one area in which the Chinese may actually have pulled ahead in what will continue to be a military chess game.In the interests of saving the world from nuclear destruction, the Chinese might choose to arm the DF-21Ds with conventional, rather than nuclear, weapons. But how, if an attack were launched on a U.S. carrier battle group, would an American commander, with 12 minutes to respond, know that? And even if the rockets carried conventional weapons, if they destroyed a U.S. carrier in international waters, how would the Americans respond?The Cuban Missile Crisis could have ignited a nuclear war had the Americans fired on Soviet ships carrying missiles to Cuba. Could a DF-21D attack on an American carrier ignite such a nuclear confrontation? At the very least, it would certainly mean war.What steps can be taken to prevent anything that destructive?A negotiated treaty between the Americans and the Chinese – similar to the Intermediate-Range Nuclear Forces Treaty between the U.S. and Russia – would help defuse things. China would surely demand some guarantees about positioning of U.S. warships in the East and South China seas, which would weaken the Americans' capacity to act as a referee between China and its neighbours.But if DF-21D is capable of doing what it is designed to do – tear apart U.S. carrier battle groups – and if the Americans do not come up with ways to neutralize it, refereeing in those seas is going to be a much more frightening occupation in the years to come at any rate. Best to know the rules of engagement.Colin Kenny is former chair of the Senate Committee on National Security and Defence. [email protected]