Secretary of Defense Robert Gates made headlines this week by announcing that "North Korea is becoming a direct threat to the United States" since it will develop an intercontinental ballistic missile (ICBM) within five years. Although the media depicted Gates's comments as a major "new assessment," North Korea's expanding missile threat to the United States and its allies has been long known. But it has been ignored, due to failures and self-imposed limitations on the part of the U.S. and its allies.

The U.S. National Intelligence Community, the federation of 17 U.S. intelligence agencies, warned in a 2001 National Intelligence Estimate that "before 2015 the United States most likely will face ICBM threats from North Korea and Iran." Using a two-stage Taepodong 2, North Korea "could deliver a several-hundred-kilogram payload . . . to strike Alaska, Hawaii, and parts of the continental United States." The NIE also predicted that a three-stage Taepo Dong would be able to reach all of North America with a payload sufficiently large to accommodate a nuclear warhead.

North Korea's 2009 Taepodong 2 test flight was dismissed as a failure because it fell short of its announced range, but it did travel 2,400 miles, twice the distance of previous long-range missile tests. That missile can still hit a target as far as near Hawaii.

More recently, the Department of Defense's U.S. Ballistic Missile Defense Review warned in February 2010 that the global ballistic missile threat is "increasing both quantitatively and qualitatively, and is likely to continue to do so over the next decade . . . ballistic missile systems are becoming more flexible, mobile, survivable, reliable, and accurate, while also increasing in range."

Diplomacy, engagement, international condemnation and United Nations resolutions have failed to stop North Korea from advancing these capabilities. Even without Pyongyang bringing out its ICBM card last year, Washington and Seoul were constrained in responding to North Korea's attack on a South Korean warship in March and shelling on Yeonpyeong island in November—they were concerned that any retaliation could escalate into a major conflict, something Kim Jong Il probably anticipated.

Kim seems interested in other provocations for 2011, and he could choose to conduct additional missile tests this year. Pyongyang probably calculates that demonstrating enhanced missile capabilities could be used as leverage against Washington and Seoul to abandon their current pressure tactics against Kim's regime. Last year, North Korea played this game of chicken when it disclosed significant progress in its uranium nuclear weapons program; it worked, as the international community grew concerned.

Clearly, the U.S. and its allies need to change tack: They should take steps to deploy sufficient missile defenses, not only to protect their citizens, but also show Pyongyang they mean business. It's unfortunate that while the North's threat has grown, the level of preparation on part of Washington and its allies has dwindled.

Despite recent deployments and technological advances such as recent successful test interceptions, U.S. missile defense capabilities "exist in numbers that are only modest in view of the expanding regional missile threat," according to the 2010 U.S. Ballistic Missile Defense Review. The fact that U.S. ships or soldiers are vulnerable to a future North Korean missile could also hinder America's defense ability here. These capabilities need to be ramped up. Washington needs to restore $1.4 billion that the Obama administration cut from the missile defense budget and resurrect the Airborne Laser, Multiple Kill Vehicle and Kinetic Energy Interceptor programs.

The U.S. can't do it alone. During the past decade, Japan has made considerable strides in ballistic missile defense. Tokyo has developed and deployed a layered integrated missile defense system consisting of Aegis destroyers with Standard Missile-3 interceptors and land-based Patriot Advance Capability-3 missiles.

But Japan's missile defenses are handicapped, thanks to legal restrictions against "collective self-defense" or defending another country against attack. So despite its technological advantage, Tokyo would not be allowed to intercept missiles attacking the United States or to protect a U.S. naval vessel that was defending Japan from missile attack—even if it was adjacent to a Japanese Aegis destroyer.

In South Korea, 10 years of liberal administrations downplayed the danger of North Korean missiles to garner domestic support for Seoul's attempts to foster reconciliation with Pyongyang. Successive presidents were also fearful that deploying a missile defense system would anger Pyongyang, lead to a collapse of the inter-Korean engagement policy, and strain relations with China. So now they have little to show for.

Since the 2008 election of President Lee Myung-bak, South Korea has been more receptive to the idea of building missile defenses, but has yet to follow through with actions. Most notably, Seoul continues to resist joining a comprehensive regional missile defense network with the U.S. and Japan.

Mr. Gates' remarks this week will be something major and new only if they trigger greater efforts to defend against Pyongyang's growing missile threat. Here's hoping that greater pressure in Washington from the new Republican Congressional leadership can convince the Obama administration to reverse cuts to U.S. missile defense budgets and programs. And that that pressure can spill over to Tokyo and Seoul too to change their respective stances on missile defense.

Mr. Klingner is senior research fellow for Northeast Asia at the Heritage Foundation.