The current crisis in South Asia has been profoundly affected by the mere presence of India's and Pakistan's nuclear arsenals.
Fighting may yet erupt over the disputed territory of Kashmir, despite the specter of possible escalation to atomic war. Indian officials, in particular, have vowed that their large conventional forces will not remain paralyzed by the threat of Pakistan's cache of nuclear bombs.
But to this point, the fact that the two adversaries are now nuclear-capable appears to have to slowed down events, as leaders in New Delhi and Islamabad gauge each other's response.
"Both sides now show great cognizance that there are nuclear dangers and that they have to be extremely careful," says George Perkovich, author of a study of India's nuclear program and fellow at the Carnegie Endowment for International Peace.
If not for the knowledge of the nuclear dangers, Indian forces on the border might have already crossed into Pakistani-controlled Kashmir, judge other experts.
Thus, for Pakistan, nuclear deterrence has worked, at least for the short term. Whether that continues, and what happens if it does not, remains to be seen.
"I know it goes against all nonproliferation theory, but I believe the presence of nuclear weapons [in the region] has actually made things better, for now," says Sumit Ganguly, a South Asia expert at the University of Texas at Austin.
The possibility of an uncontrolled India-Pakistan war over Kashmir has long been a nightmare scenario for Western non-proliferation experts. It represents the most likely set of circumstances they can think of that could lead to the use of a nuclear weapon in anger.
The human toll of such an attack would be unthinkable. India has more than 1 billion people, and Pakistan nearly 150 million. Just one weapon detonated over Bombay could cause 850,000 casualties, according to a recent study.
And in recent years, India and Pakistan have engaged in worrisome rounds of nuclear bluster.
In May, 1998, India conducted what it described as five nuclear tests in the northwestern desert state of Rajasthan. The tests were India's first since 1974, and ended a careful stance of ambiguity regarding the nation's possession of nuclear weapons.
Three weeks later, Pakistan conducted six nuclear tests in its southwestern region. The point: we can do it, too.
The United States and the Soviet Union also engaged in such nuclear showmanship, particularly at the beginning of the cold war. But the superpowers' capitals were not three or four minutes of missile flight time apart, as are New Delhi and Islamabad.
Nor did superpowers' troops ever fire directly on each other in an extensive hot war. India and Pakistan now have tens of thousands of troops facing each other across their mutual border, mobilized since a Dec. 12 attack on the Indian Parliament, which India blamed on Pakistan-based Kashmiri terrorist groups.
Tensions have eased a bit in recent days, as both sides have suggested diplomacy could end the crisis.
"War is not a must," said Indian Prime Minister Atal Behari Vajpayee prior to leaving for a regional summit yesterday in Nepal.
India's nuclear-weapons program began in earnest after its defeat in a 1962 border war with China. Since then, much of its arsenal has been developed as a counterweight to Beijing, as much as a deterrent to Islamabad.
Today, India has a small stockpile of nuclear-weapon components, as opposed to assembled, at-the-ready weapons, according to the CIA. It could assemble and deploy them within a few days or a few weeks.
"The most likely delivery platforms are fighter-bomber aircraft," writes Anthony Cordesman, a military expert at the Center for Strategic and International Studies, in a recent report. "New Delhi also is developing ballistic missiles that will be capable of delivering a nuclear payload in the future."
India has declared that it will not be the first to use nuclear weapons in the region. It has also expressed interest in obtaining a US-style triad of nuclear-capable aircraft, missiles, and submarines.
Pakistan's program, by contrast, is directed solely at deterring India. Its roots lie in the frustration of Pakistani officials at their defeat in a 1965 India war. Then-Foreign Minister Zulfikhar Ali Bhutto famously declared that Pakistan would match India's nuclear progress "even if we have to eat grass or leaves."
Experts estimate that today, Pakistan has anywhere from 24 to 48 nuclear weapons. US-made F-16s are the likely mode of delivery, although in 1998 it flight-tested a single-stage Ghauri-1 missile that is thought to be nuclear capable.
In 1990, amid tensions in Kashmir not dissimilar to those of today, US satellites detected a convoy of trucks leaving a Pakistani nuclear site and heading toward an air base, according to a New Yorker magazine article by the investigative journalist Seymour Hersh. American diplomats informed India of this development, and India pulled back its troops, according to the article.
Since then, Western experts have cast much doubt on this report. But it has become an article of faith among Pakistani hawks that their nuclear arsenal has provided useful deterrence against India.
Lending credence to their belief were Indian actions during the 1995 fighting centered in the Kargil area of Kashmir, in which Indian warplanes were careful never to cross into Pakistani-controlled territory.
This perception does not sit well in India. In the current crisis, Indian officials such as defense minister George Fernandes have gone out of their way to state that they believe Pakistan would not respond to a conventional attack with a nuclear one, as subsequent retaliation would be too devastating.
Says Mr. Perkovich of the Carnegie Endowment: "Some of the determination now in India is to show that they're not afraid of war."