Zhang Liangui, professor of international strategic research at Central Party School in Beijing, said:

Despite signing treaties on non-proliferation, "North Korea never stopped its nuclear program" from the 1960s, and instead kept buying time. "The balance of comprehensive national strength began to tip in the early 1970s, and widened dramatically with the South's economic power growing 30 times greater than the North," he says.

"North Korean leaders see mastering nuclear weapons as the only possible measure to dispel the fear of failure in this competition, and even possibly to take the initiative in unifying the Korean peninsula though force."

– The Australian News

I think his reading of the situation is right on the money. Unfortunately, a complete embargo will force North Korea to explode southward like an over-squeezed tube of toothpaste. Ally or not, expect South Korea to stay neutral in the coming embargo. But then it might be years from now if Kim Jong-Il continues to be successful in buying time.