WHY US AND OTHER WESTERN POWERS RESENT NUCLEAR TESTS BY NORTH KOREA?
Western powers have monopolized the nuclear power and weapons. Russia and US hold 92% of the resources. Treaties like CTBT discriminate against the rest of the countries who want to use nuclear resources even for peaceful purposes. India has not signed this treaty. Supply of nuclear materials is controlled by Nuclear Supplies Group (NSG) which is largely controlled by US and Russia and puts discriminatory conditions on developing nations.This is why they are bitterly opposing nuclear tests by North Korea who is not toeing to their line.
Here are statistics
No. of nuclear tests:
USSR Russia: 715
North Korea: 6