Iran is pursuing a nuclear program that clearly goes beyond peaceful, civilian purposes, though the U.S. intelligence community assesses that Tehran has not yet decided to build a bomb, only to have the capability to do so. North Korea, on the other hand, has tested nuclear devices three times since 2006. So why do the United States and international community usually focus more attention on Iran than on North Korea?

Two reasons explain this. First, the international community is more likely to affect Tehran’s calculus than Pyongyang’s. Second, the proliferation ramifications of Iran getting a nuclear weapon would be much worse.

North Korea and Iran are both under UN Security Council sanctions for their nuclear programs. The United States has led the way in applying additional sanctions on the two countries.

North Korea, however, has a poor, autarkic economy. The CIA World Fact Book estimated per capita gross domestic product in 2011 at $1800. North Korea has limited trade with the outside world. In 2011, the CIA put its total trade turnover at less than $9 billion; two-thirds of that was with China, which has been reluctant to apply a real economic bite to North Korea. The impact of sanctions on North Korea’s largely stagnant economy to date is difficult to see.

Iran, on the other hand, is a richer country and far more integrated into the global economy. The CIA estimated per capita gross domestic product in Iran at just over $13,000 in 2012 and put its trade turnover in 2012 at $133 billion. Oil is Iran’s main export commodity. Recent energy trends— including development of unconventional gas and oil deposits in the United States and soft global energy demand— have allowed countries to curb their imports of Iranian oil, which make up 80 percent of Iran’s exports. The CIA estimated that the country’s total exports fell from $129 billion in 2011 to $66 billion in 2012. The financial and other economic sanctions are having a bite; Iran’s currency, the rial, lost 40 percent of its value in one week last fall, and the country’s gross domestic product declined for the first time in some 20 years.

How this all affects Tehran’s calculations remains to be seen. The West hopes that the Iranian government will not be able to ignore the sanctions’ effect on the economy or the political impact as falling economic standards provoke popular disgruntlement. In any event, the effect in Tehran is certain to be greater than in North Korea, where a large portion of the population barely ekes out a living and probably sees no incremental economic effect from the sanctions applied on their country.

The second reason for a focus on Iran is the potential ramifications for the Non-Proliferation Treaty (NPT) should Tehran develop a nuclear weapon. That would be a game-changer in the Middle East, leading other countries in the region, such as Saudi Arabia, Egypt and Turkey, to consider whether they should acquire nuclear weapons as well. In the worst case, the emergence of four new nuclear weapons states in the region would put huge stress on the NPT regime. And with these four states, plus Israel, having nuclear weapons, the Middle East would become a far more volatile region.

To be sure, North Korea’s possession of nuclear weapons puts the NPT regime under stress— but not as much. The two countries in the region most concerned, South Korea and Japan, have long been American allies under protection of the U.S. nuclear umbrella. The U.S. military deployed tactical nuclear weapons in South Korea until the early 1990s, and the B-2 overflight during the March tensions with North Korea provided a pointed reminder that the U.S. strategic nuclear arsenal still protects the country. While some in South Korea and Japan have pondered whether their countries should go nuclear, the governments appear reassured that the U.S. nuclear guarantee remains and that they do not need nuclear weapons of their own.

Should Iran get nuclear weapons, the United States might seek to extend a nuclear umbrella in the Middle East. Former Secretary of State Clinton suggested that possibility several years ago. Turkey has long rested under the nuclear umbrella provided by the United States to NATO (and reportedly hosts U.S. nuclear weapons). But would it work with other states in the region, which have not had nuclear security arrangements with the United States that go back decades?

Iran may feel that it is being unfairly singled out. Perhaps. Life, particularly life in international politics, isn’t fair. But the United States and international community have a clear rationale for doing so. A nuclear-armed Iran would put more stress on the nuclear non-proliferation regime than does North Korea. And the chances that sanctions may have an impact on Tehran’s calculations are far greater than in the case with Pyongyang.