you forgot one: meteorite specifically 'armageddon' movie meteorite

No I'm being serious, cant u tell this is my serious face...

I am sorry, but I disagree with your premise I don’t see Islam as a threat at all. I have a little insight to this as my sister was Muslim and growing up in a house that was religiously diverse was interesting.
The reason I don’t see Islam as a threat is because it is religion not a nation of people bent on the destruction of the world, like the Nazi, Communist, or any Imperialist nation. There are nutcases out there that want to see it happen. The President of Iran believes that it is his job to bring about Armageddon in order for the 12th Imam to return and bring peace. So he supports terrorism and any other form of anarchy. But you have people throughout history that have tired that in every religion. The AUM Shinrikyo (Supreme Truth) leader promised the end of the world and when that did not happen he convinced his followers that it was their job to bring about the end of the world. They bombed and gassed people around the world in order to bring it about. These are cults and splinters of religions not the religion itself. Thousands of people around the world are murdered with knives yet there is not anyone that wants to ban knives or see them as a world wide threat. The people that do murder are nuts and people move on. Christians did the crusades and tried to convert the world by force. It was wrong and it thankfully stopped. 1400 years later Islamic nuts are trying to do the same thing, God willing it will fail as well.

I suppose there are others, on JU who believe that Islam is a threat and that's why it was included. I can see you are still working out the nuts and bolts of how to rank the other 3.

"Like the US, Russia is still functioning under a Cold War mentality"

Russia is interested in making money, not fighting another cold war, which was lost by the Soviets by the way.

"The Cold War is still costing us lives."

In what way?

"These are useful against fixed wing aircraft, helicopters, UAVs, and guided missiles. Given the need for Iran to defend it's adolescent nuclear arms program, the timing could not possibly be worse, and it is anything but "defensive"."

Useful against fixed wing aircraft flying very low, low, or at medium altitudes, anything upwards of 25,000 feet would be fine no matter how large the aircraft or how un-stealthy. Fact is good for Iran. Sink as much money into these systems as you like. The F-22 which would be leading the charge and taking these things out paving the way for other aerial bombardment, is virtually impervious to this weapons system. Not only would this weapons system not be able to detect the F-22 until the F-22 attacked and destroyed it, but even if the F-22 chose not too and flew right through the Weapons engagement zone, it would be at risk for a very few seconds. The F-22 pilot could also choose to jam the hell out of this weapon system rather then attack it, and allow another unit to attack it. So the timing for Iran is perfect. If Iran doesn't cooperate with UN resolutions and with the world body, on the "No Nukes for Iran" policy, they can expect an attack they cannot defend against. Wasting even more money in the fruitless pursuit of nuclear weaponry.

UAV's by the way cannot carry the munitions necessary to destroy an underground or even above ground fixed installation, i.e. building. helicopters cannot carry the munitions either. "

It is not the magnitude of the threat, but the resolve of the people to deal with it. None listed would be a problem if the resolve was there from the start of the threat. And none would amount to much if the resolve of the people to deal with the threat is there to handle it once the threat is going full bore.

However, it is the ignoring of the threat that creates the crises. And if that is not dealt with once it hits the crises stage, then that threat will be the greatest as it will lead to the destruction of the threatened society.

I'll have a go, though understandably its difficult to compare these things, and understand why people have chosen not to.

1 Communism, way out in front. Leads the pack because the stated goal was worldwide communism, and had the backing of a nuclear armed superpower (even though a communist world in its purist form wouldn't have any nation states). Not so much the threat of physical violence from arms as the thought of the whole world living under communism, which is clearly not an optimum form of economic or political society. Had the misfortune of taking on a stronger ecomomic power.

2 Nazism. In my view a better social and economic system (than communism) for those that lived under it (with the obvious exception of its victims), otherwise the Germans themselves might have tried to get rid of it. Inextricably linked to Hitler, would have been nowhere near as powerful if not for him. Also had the backing of a strong nation state. However was never going to beat the USSR realistically, (otherwise it might have been top of this list).

3 Japanese imperialism. While like Nazism it too had the backing of a strong nation state, it couldn't overcome a weak and divided China. I doubt it would have tried to take on the European powers if they had not been weakened by the Nazis first. This of course led to its downfall anyway, so while living under the Japanese would have been hell, they simply didn't have the means to pull it off. Even Yamamoto didn't think they could.

4 Radical Islam. While probably more unattractive than any of the above, like the Japanese it simply doesn't have the means to achieve its goals. While radical islamist groups (eg Hezbollah) do have the backing of nation states, even Iran doesn't ask it to do anymore than attack Israel. There is no one strong leader of the Islamic world, let alone one of the radical islamic world. Power is still concentrated amongst the nation states, which limits radical islam's access to it. Not to mention the divisions among Islam itself. For this reason I place it 4th, though that's not to say its not dangerous, or poses no threat whatsoever.

5 Meteorite. Bruce will save us, won't he?   

Oh sorry guys, this latest post by me was just, me dropping my 350 word response to somebody, without realizing I'd been blacklisted, it doesn't exactly tell you in advance:Thanks Startdock...

Anyway.

"it is the ignoring of the threat that creates the crises." I agree, however there have been times in history we have chosen to be untruthful with nations that would get us involved in conflict, i.e. Hitler before WW2, and Hussein before Gulf War I.

"Also had the backing of a strong nation state. However was never going to beat the USSR realistically, (otherwise it might have been top of this list)."

If Hitler had been able to secure peace with Britain before attacking Russia, and if the Japanese had not attacked the United States, or had attacked with proper warning, Hitler might have been able to concentrate additional troops on the Eastern front and won Moscow, as well as St. Petersburg. Eliminating the USSR. The United States might very well have just engaged the Japanese had the British been assured peace. It was good for world history that Britain had a very staunch leader in Churchill or they might well have accepted less then unconditional surrender by the Germans or even peace, sacrificing France, Poland, Czechoslovakia, Finland, Norway, Luxembourg...etc.

"5 Meteorite. Bruce will save us, won't he? "

LOL.