No wonder gleeful North Korean leader Kim Jong-un was having such a big laugh. It's not often that a small nation of only 24.8 million can defy the mighty United States, Japan, South Korea and even its sole ally, China. But Kim did, and survived the experience.

North Korea fired off its fifth underground nuclear device estimated at 15-20 kilotons. The detonation was estimated at around the same size as the US nuclear devices that destroyed Hiroshima and Nagasaki in 1945.

What made this test different was the announcement by Pyongyang that it had 'standardized' production of nuclear warheads and, even more important, reduced their size and weight so they could be fitted atop medium and long-ranged missiles. Previous North Korean nuclear devices were believed too heavy and bulky to be delivered by missiles.