Mr Hwang was speaking at a long-awaited news conference in Seoul, his first public appearance since April, when he arrived in the South, two months after defecting through the South Korean embassy in Peking. Since then, he has been undergoing an extensive "debriefing" by South Korean's spy organisation, the Agency for National Security Planning (NSP).
As a senior member of the North Korean Worker's Party, a former tutor to the country's leader, Kim Jong Il, and its leading political philosopher, he was expected to provide unprecedented new insights into the workings of one of the world's most secretive and unpredictable regimes. But three months of questioning have produced a remarkable result: on almost every aspect of North Korea, Mr Hwang and his new government are in perfect agreement.
The message sent by Mr Hwang is the one which successive South Korean governments have been repeating to their people and allies for decades: for all the food shortages and economic crises which have beset the country recently, North Korea's leaders are psychopaths, bent on invading the South Korean paradise at the first opportunity. Mr Hwang's vehement denunciations of the country he served for 60 years were matched only by his praise for his new home.
"I have come to the Republic of Korea (ROK) to warn about the danger of an armed invasion of the South and to contribute to the peaceful unification of our country," Mr Hwang said in a prepared statement. "The North's preparedness for war goes beyond imagination. North Korea is permeated by an atmosphere of war ... I am firmly convinced that it is necessary for all Koreans to be firmly united and thoroughly prepared if we are to prevent the impending war and safeguard freedom and peace."
In a separate written statement, issued on his behalf by the NSP, Mr Hwang described the invasion strategy devised by Kim Jong Il, the son of North Korea's founding "Great Leader", Kim Il Sung. This would begin with a faked attack by North Korean troops wearing South Korean uniforms, thus providing the pretext for an artillery bombardment of Seoul. Any American intervention on behalf of the South would be punished with a missile strike on Japan which would "turn the area into a sea of fire".
Strategic facilities in the South would be seized by 100,000 commandos, followed by a full-scale motorised invasion, which would seize control of Seoul within a week, and the entire country within six months.
If such a plan does exist it will bring little anxiety to American officials who say that an attack by North Korea's poorly equipped and under-fuelled forces, while highly destructive, would be repulsed in a matter of days. According to Mr Hwang, Kim Jong Il wanted to attack the South in 1992, but was talked out of it by his late father.
This week, the United Nations launched another appeal for $45.7m worth of food aid to alleviate food shortages in North Korea. Meanwhile in Pyongyang, Kim Jong Il made a rare public appearance at ceremonies marking the third anniversary of his father's death. Mr Hwang confirmed that the country is suffering from wide-spread food shortages, and that Kim Jong Il is in firm personal control. But on several crucial questions, he was disappointingly vague.
In April, Mr Hwang was quoted as having told the NSP that Pyongyang was capable of "scorching" Seoul with nuclear missiles. But yesterday he admitted that, as a party intellectual rather than a military commander, he had never seen such a weapon. "It's common sense that there are [nuclear weapons]," he said. "I just can't prove it."
He also poured cold water on rumours of the so-called "Hwang list", said to contain the names of hundreds of senior South Koreans working as spies for the communist side, but insisted that "there are operations sections engaged in infiltration and intelligence".