Iraq is a completely different story. Saddam Hussein had been an USA ally for decades. Bought (chemical) weapons from the USA. And in 2003 shifted his trade in oil from US Dollars to Euros. Compare this with North Korea. China have been an ally for decades, backed with an military alliance pact. Russia has been a less closer ally, but still, trough the SCO it's indirectly supporting North Korea, and has to act in case of an foreign attack on North Korea.