Why india is not conducting another nuclear test
Answers
One of the reasons why other countries could not stop India was the clandestine nature of the whole program. The American intelligence agencies were embarrassed and the chairman of the Senate Intelligence committee had termed it as "a serious intelligence failure of the decade" in detecting the preparations for the Pokhran II test. Following is a brief history of India's nuclear programme:
Steps taken by the International community after Pokhran I (Smiling Buddha)
In response to India's test, the Nuclear Suppliers Group was formed in 1974. It was noted that formation of nuclear weapons required certain set of materials, equipment and technical know how. Countries were discouraged to export any such material or equipment. India's nuclear program was crippled due to lack of indigenous technology or material. Most countries even today rely on imports to convert non-weapons specific nuclear technology into weapons development.
The first article of Non Proliferation Treaty (NPT), restrains Nuclear Weapon States (NWS) from transferring "nuclear weapons or other nuclear weapons devices" to a non-nuclear weapon state (NNWS). The world's major nuclear powers imposed nuclear embargo on India.
The US intelligence agencies had tried to keep a constant watch on India. In 1995, Prime Minister P.V Narasimha Rao decided to carry out further tests. But the plans were halted after American satellites picked up signs of preparations for testing at Pokhran. The Americans under president Bill Clinton exerted enormous pressure on Rao to stop the preparations.
Pakistan government continuously issued harsh and severe statements to build international pressure.
Preparations for the Pokhran II test
Since it was very difficult for India to hide activities from a probing satellite in the sparse terrain of Rajasthan desert, utmost secrecy was required.
The 58th Engineer Regiment of the Corps of Engineers of Indian Army was commissioned to prepare the test sites without being probed by the US spy satellites.
Extensive planning was done by a very small group of scientists, senior military officers and senior politicians to ensure that the test preparations would remain secret, and even senior members of the Indian government didn't know what was going on.
Since 1995, the 58th Engineer Regiment had learned to avoid satellite detection. Work was mostly done during night, and equipment was returned to the original place to give the impression that it was never moved.
Bomb shafts were dug under camouflage netting and the dug-out sand was shaped like shaped dunes. Cables for sensors were covered with sand and concealed using native vegetation.
The scientists and other officials would not depart for Pokhran in groups of two or three. They travelled to destination other than Pokhran under pseudonyms, and were then transported by the army.
They were all dressed up in army uniforms to prevent detection by satellites.
Although there was criticism after the test but as pointed out by Balaji Viswanathan the world accepted the reality for a variety of reasons. Most importantly Pakistan's nuclear test strengthened India's case.
Note: In 1974 India's nuclear program was not militarized (no weapons). The militarization had been authorized by Indira Gandhi but the program lost momentum due to Emergency. On the other hand Pakistan's nuclear program during this period (post Pokhran I) was under military guidance and well funded. Pakistan's program was the main motivation behind Pokhran II.
The inherent flaw in NPT and how countries make nuclear weapons secretly
The problem arises because of Article I and and Article IV (2) of the NPT -
The Article I says - Each nuclear-weapons state (NWS) undertakes not to transfer, to any recipient, nuclear weapons, or other nuclear explosive devices, and not to assist any non-nuclear weapon state to manufacture or acquire such weapons or devices.
The Article IV (2) says - All the Parties to the Treaty undertake to facilitate, and have the right to participate in, the fullest possible exchange of equipment, materials and scientific and technological information for the peaceful uses of nuclear energy.