When America declares war on North Korea, North Korea would plan to nuke us with their hydrogen bomb, but their missile could not reach to America. America would build a nuclear defense missile system in South Korea. A North Korean wants to be friends with an American, according to CNN. There would be no more DMZ and no more fear of North Korea and their nuclear weapons. Even though they might lose the war, they will not lose another war because they have more, advanced technology and better, trained soldiers than North Korea. America has about 11,000 air power and US has about 4.5 k navy power. North Korea has 944 air power and 1061 naval strength. America has better military strength than North Korea. North Korea produces 44 gallons of oil a day and America produces 4.1 million barrels of oil a day. America has enough resources to defeat North Korea. America has about 151 million soldiers and North Korea has 10 million soldiers. America is going to outnumber North Korea. After the war, North Korea might team up with America to defeat ISIS and they can trade America their nukes for America's advanced war technologies. North and South Korea might be friends with each other.
North Korea has a lot of nukes, and are capable of the HYDROGEN BOMB. If we just wait, they are going to take that as a sign of fear, and wreck the rest of the world, causing World War 3 or a nuclear war. As the second reply for against, no, we might not be friends with North Korea, but it will stop them from wrecking everything we know and love. U.S. also will have powerful allies fighting with them(Great Britain, South Korea, maybe even Germany or Ireland). India would also probably be supporting America. We have nothing to worry about, nor are we going to do bad.
Going to war with a country that has nuclear weapons and is allied with countries such as China and Russia (As the previous opinion explained) wouldn't be a very intelligent idea. It would be far more sensible to try and talk things out peacefully rather than screaming "AMERICA!" and attacking them.
Though the United States may have greater military power, North Korea is allied with several other countries, namely Russia and China. A military invasion would not end well for either side and also if there are actually "North Koreans that want to be friends with USA", shooting them would not make them your friends, it would kill them. A land invasion would costs America much money and also lives as the North Koreans would likely fight to the last man, woman, and child.
Hojina102 mentions that North Korea's hydrogen bomb can not reach USA but it could likely reach Seoul which is only 34 miles away costing South Korea many lives. There have been very few wars, if any in the past decades, that have been between to nations. Most current wars are civil wars or local conflicts. A full-blown war between nations would cause immense instability in the world as if America ever goes to war North Korea many nations would soon follow.
If the war is won by the Americans what then? The citizens of North Korea would not just simply become friends with South Korea and US, especially not after we just invaded them. Hojina102 also mentions at the end of his argument that North Korea would do this and that, my question to that is why. If there is ever a war why would America just let North Korea remain a sovereign state. America would not "trade military hardware for nukes" as that would just equip North Korea the means to start another war.
All in all, an invasion of North Korea is simply unrealistic and against the interest of all factions.