Why was India not stopped from testing nuclear arms by the the US and other countries of the NPT?

America and other western countries tried their best to stop India from doing another nuclear test.

India has used CIRUS nuclear reactor (that was supplied by Canada & it used American Heavy water) for producing weapon grade plutonium for its 1st nuclear test on 1974. India had verbally assured that India would only use the reactor for peaceful purposes. There was high outrage over Indian nuclear test & NSG (Nuclear Supplier Group) was formed in reaction to the Indian tests to check international nuclear proliferation. After 1974 tests, India hardly received any western support in its civilian nuclear program.

Americans always wanted to prevent nuclear test by India & Pakistan. They had put a satellite specially to detect Indian nuclear test preparation. India had plan to test nuclear device in 1995 but the preparations were detected by American satellites. President Clinton is said to have spoken personally to PM Narasimha Rao to dissuade him from testing in 1995 & American ambassador warned India of dire economic sanctions. Then Narasimha Rao told PM Atal Bihari Vajpayee that the bomb was ready. He just need to exploded it. This time Indian scientists were fully ready & they fooled American satellites and conducted Nuclear tests in full secrecy.