North Korea’s million-man army may look impressive on paper, but remember that Iraq had a million-man army, which also had modern equipment, combat experience, and plenty of fuel.
In contrast, North Korean soldiers suffer from malnutrition and rarely train due to a scarcity of fuel and ammo. Most North Korean soldiers could not attack because they are needed to defend the entire DMZ and coastal approaches (they remember the 1950 landing at Inchon) while entire divisions must remain throughout North Korea to fend off heliborne offensives, food riots, and probable coups.
On the other hand, the entire 700,000 man South Korean active duty army can be devoted to the defense of Seoul. The modern South Korean army is backed by over 5,000,000 well-trained reservists who can be called to duty in hours. South Korea has twice the population of the North, thirty times its economic power, and spends three times more on its military each year.
South Korean military equipment is first class whereas most of the North Korean military equipment is over 30 years old and much is inoperable due to a lack of maintenance. If war broke out, South Korea has a massive industrial capacity and $94 billion in foreign currency reserves to sustain a war, while North Korea has no industry and no money. As a result, South Korea is roughly five times more powerful than North Korea.