Peace in South Asia, home to the poorest one-sixth of humanity, and the future of global disarmament have been plunged into uncertainty by Pakistan's detonation of five nuclear devices in response to five by rival India.
In setting off the devices yesterday in an underground shaft at a site in the remote Chagai region, Pakistan ignored threats of economic sanctions and pleas for restraint by President Clinton.
In authorizing the blasts, Prime Minister Nawaz Sharif bowed to intense domestic pressure stoked by national pride and demands he ensure Pakistan's security. But he warned the 140 million Pakistanis that sanctions could create food shortages, restricting many to one meal a day.
These tests by India and Pakistan have transformed the global balance of power within 17 days. The two have joined five other countries - the United States, Russia, China, Britain, and France - in acknowledging they have nuclear weapons.
By doing so, they have brought the threat of nuclear annihilation to hundreds of millions of people. And as they develop missiles capable of lofting atomic warheads, they pose threats to other parts of Asia and portions of the Mideast.
But just how the new nuclear order will evolve remains unclear.
The new Indian-Pakistan nuclear capability adds to the uncertainty that has marked international developments since the end of the US-Soviet rivalry.
Many experts fear the tests will fuel an upsurge in the rivalry between Pakistan, an overwhelmingly Muslim state, and predominantly Hindu India. The two nations have fought three wars since they won independence from Britain in 1947. They came close to a fourth conflict in 1990 over Kashmir, a divided Himalayan region where the foes engage in near-daily clashes that US officials say have intensified since India's tests.
A war of words has also escalated in recent days, reaching new heights yesterday when Pakistan accused India of preparing to attack its nuclear facilities. New Delhi denied the charge.
The Pakistani test "takes us yet another step ... up the ladder of increased tensions in the South Asia region," says a US official, speaking on condition of anonymity. "It makes the security situation in the region even less controllable."
Such concerns are being stoked by aggressive missile development programs on both sides. In addition, neither country has a strategy for employing nuclear weapons, command-and-control systems, or civil defense measures.
Both face other tough calculations. Aside from the certainty of retaliation for a nuclear attack, both must grapple with the reality that by using atomic arms within the narrow confines of the Indian subcontinent, they risk killing many of their own people from radioactive fallout blown back across their border by the winds.
"The real dangerous time will come as both countries put the command structures and strategic systems in place for an effective nuclear deterrence," warns Sandy Gordon, author of "India's Rise to Power in the 20th Century and Beyond."
In Washington, Clinton said he was invoking a US law requiring him to impose on Pakistan the same sanctions that he slapped on India after it tested. He deplored Pakistan's decision, saying it had wasted "a truly priceless opportunity to strengthen its own security and to improve its political standing in the eyes of the world."
The US had been scrambling since India's tests to compile a package of incentives to persuade Pakistan not to respond with its own, including economic assistance, a resumption of conventional arms sales suspended in 1990, and other security-boosting measures. Clinton himself sought to persuade Sharif to exercise restraint in four telephone calls, including one he made only hours before the Pakistani detonations.
The US sanctions require a cutoff of American private and government loans to Pakistan. The US will also oppose new multilateral loans on which Pakistan, which has only $1 billion in hard cash reserves and massive debts, is critically dependent.
"History had placed us at a crossroad. One road took us toward challenges and the other towards slavery and subjugation" said Sharif in a television speech yesterday. "We chose to sacrifice and secure our freedom."
The US this week forced the World Bank to indefinitely delay $865 million in loans to New Delhi. But India's economy is far stronger than that of Pakistan, leading some experts to conclude that one of India's calculations in testing was that its rival would be sucked into fiscal suicide by following suit.
"Pakistan has done exactly what India wants," says Dr. Gordon.
Another major unknown is how China, which for years has aligned with Pakistan to contain India, will respond to the new nuclear equation. It declined to condemn the Pakistani tests, contending that "the current situation in South Asia was created solely by India."
Some experts worry that India's tests may push Beijing's communist leadership toward renouncing its signature of the 1996 Comprehensive Test Ban Treaty (CTBT) and end a suspension of underground blasts as part of an ongoing nuclear-modernization program.
China battled India in a 1962 war in a border dispute that remains unresolved. It has played a critical role in aiding Pakistan's clandestine nuclear weapons program, according to US officials, who say it provided Islamabad with technology and know-how to develop warheads and missiles.
In the longer term, many experts fear that the failure of the world's powers, particularly the US, to preempt Indian and Pakistan tests with effective diplomacy could encourage other states with nuclear ambitions to pursue the development of atomic weapons.
Yan Xuetong, a scholar at the China Institute for Contemporary International Studies, said that "countries in the Mideast could see the latest tests as a window of opportunity to become a nuclear state." The only nation in the Middle East believed to have developed nuclear arms is Israel, and it has long feared the appearance of an "Islamic bomb" that Pakistan has now created.
And earlier this month, North Korea threatened to restart its nuclear program due to a dispute over the Geneva accord with the US, Japan, and South Korea that froze the North's feared moves toward becoming a nuclear power.
* Contributors John Zubrzycki in New Delhi and Farhan Bokhari in Islamabad, and staff writer Kevin Platt in Beijing, provided material for this report.