North Korea is a Stalinist police state that is desperate to stay in power. North Korea has run drugs in the past to keep their ramshackle economy going. Currently, the North Koreans sell weapons of mass destruction to anyone with cash. The North Korean economy has been in free fall since the end of the Cold War cut off Russian subsidies. Several severe droughts and a typically inept communist economy have killed over a million North Koreans (mostly from disease and malnutrition.) It appears that the North Koreans are finally implementing economic reforms urged on them by the Chinese (who were in similarly bad shape 30 years ago.)
Iraq is a dictatorship under UN embargo and in violation of ceasefire accords signed in 1991. According to arms inspectors (since expelled) and defectors, Iraq has developed and manufactured chemical and biological weapons, and is trying to build nuclear weapons. Since Iraq is run by the Sunni minority (about 20 percent of the population), it has used terror and mass murder to stay in power.
Perhaps because Iraq has the weakest armed forces of the three, and is the most likely to provide chemical and biological weapons to terrorist groups, there has been much discussion in the American government about invading Iraq and replacing the dictatorship with a democracy. This has generated a great debate over the pros and cons of invading. The usual arguments for the invasion concentrate on the chemical, biological and nuclear weapons, and the homicidal instability of Saddam Hussein. He's invaded two of his neighbors in the last 14 years and used chemical weapons against his own people. Or, to put the pro-invasion argument a different way; the Iraqi people deserve better. The arguments against invasion concentrate on the fact that most nations in the world are against such an operation, and the likelihood that an invasion would inflame the Moslem world. Plus it would cost a lot of money and keep an American occupation army tied down in Iraq for years, assuming the U.S. won.
The pro-invasion crowd responds with a "so what." They feel that the Iraqi people are tired of Saddam and would quickly welcome an invading army. Nothing succeeds like success, and the outraged Arab world would be as mortified as they were when the Afghan people welcomed an American invasion. As for the cost, an invasion is cheaper than a biological weapons attack on the United States with Iraqi supplied material.
But there other, less discussed aspects to all this. First, there is the danger of Iraq giving terrorists chemical or biological weapons. Keep in mind that none of these weapons is as lethal as a large bomb. The only exceptions would be smallpox or some similar bioengineered disease that spreads fast and kills quickly. But the number of terrorist groups that would use such a weapon is small. That's because such a weapon would quickly spread to the populations the terrorists are supposedly fighting for and kill millions of the terrorists supporters. Only terrorists who are out to destroy the world would have a reason to use this approach. Such groups exist, but they are few and usually very small and ineffectual. OK, what about biological weapons like Anthrax? You don't need Iraq to supply you, as you can find Anthrax in the wild throughout the world. Some technical expertise is required to find and grow anthrax for terrorist attacks. But it's basically a low tech operation. While the bad guys are at it, they can also acquire some hoof and mouth disease. This stuff is a virus and can be easily smuggled into the United States, where it could devastate American agriculture, killing millions of cattle, cows, pigs and horses. The cost to the U.S. would be in the tens of billions. Like Anthrax, there's no blow back to your own nation. And for Islamic terrorists, there's added satisfaction in killing all those pigs. The Islamic terrorists also have the an opportunity to blame the attack on militant vegetarians or the PETA crowd. None of this requires Iraqi cooperation.
There are also unspoken reasons why Iraq's neighbors, and the rest of the world, oppose an invasion. Removing Saddam by military force scares the other leaders of the Arab world because it might (and probably would) work. If such an operation also managed to install a functioning democracy (not a sure thing) it would show the citizens of other Arab states that there is one sure fire way to get rid of the local tyrants and install democracy. Such a development is also anathema to Islamic militants, who want to replace Arab dictators with "Islamic Republics" (run by the clergy.) Most Arabs don't want this, and the militants know it. Europeans are against the invasion because, if it works, it brings back ugly memories of European colonialism that was supposed to benefit the victims, but didn't. There's also some fear that past secret deals with Saddam will come to light. Finally, Europeans hate it when America does something Europeans either didn't think of, lacked the will to try or the gumption to make it work.
Perhaps more than anything, invading Iraq would be something different, and most people simply fear the unknown.
The War on Terror is shifting from Afghanistan to Iraq. The United States has identified Iraq, Iran and North Korea as rogue nations most likely to support terrorism in the future. Iran is, technically, opposed to terrorism, but has a rather strange domestic political situation. While moderate democrats (many of them pro-American) comprise the majority of the population, the constitution gives religious conservatives (who openly support terrorism) veto power over anything the parliament or prime minister does. The moderates are trying to put the Islamic militants out of business, but most Iranians do not want another civil war, at least not yet.