I’ve recently had a little bit of time on my hands during a train ride, so I thought a bit about the “secret war” concept that has been discussed in the forums.
Firstoff, two assumptions:
The aliens are basically bound to the physical laws known to us. This is necessary to have any discussion at all, else anything becomes a question of tech-mcguffinism.
The aliens have a solid reason to take over the Earth. If they just eventually want a habitable planet, it would probably be more effective to just terraform mars, if they already have the energy necessary to travel from one solar system to another with a sizeable fleet. If they merely want “the superiour human race” (*cough-Firaxiscom-cough*) it would be less effort to just get a couple of specimens and work with cloning / genetic engineering.
The entire concept of aliens wanting to cause a nuclear war seems a little absurd: if all they want is to render Earth uninhabitable, just redirect a couple of asteroids from the asteroid belt to hit Earth. That way you don’t even have to worry about thousands of years of nuclear contamination before Earth becomes colonizeable again. Since the aliens come from another solar system, doing this should be no technical challenge to them, and to this day we do not have any reasonable defense against such an incident.
A few real life facts:
In 1990 the US had in excess of 20 000 nuclear warheads, while the USSR had more than 30 000. These were mostly strategic nuclear warheads, since the INF-Treaty from 1988 forbid short and intermediate range nuclear warheads for land forces (reducing the total number of nuclear warheads significantly). Current estimates state that as few as 100 nuclear explosions from strategic warheads would probably be enough to render Earth uninhabitable – granted, the aliens likely would have more effective ways to deal with some of the primary problems, like getting rid of the particles that would cause nuclear winter, so let’s multiply that number by 10. That means that either the US or the USSR might loose 90% of their nuclear assets and could still easily render Earth uninhabitable. A second issue to consider is that for this strategy to work it is not necessary that the warheads are launched or delivered to a specific target – they can be detonated inside their bunkers or right after launch. Even if intercepted, there would be a non-negligible chance for the weapon to detonate regardless. As such it can be stated that even if the aliens possessed the capability to intercept every single missile fired at them, the US and USSR governments would be in a position where they are capable of rendering Earth uninhabitable.
During the Cold War, the official stance of politicians was that they were willing to accept complete annihilation rather than domination from a different political power. As such, even if the humans had no effective way of attacking an alien fleet in orbit, they could essentially take the planet Earth hostage and threaten that if they loose the war, no one will win.
As a practical example of this strategy actually working, consider Sweden’s neutrality during WW II. The Swedes threatened that if invaded, they would flood their ore mines, which proved an effective deterrent given that all parties of the war were interested in trading ore with Sweden.
Now off to speculation. The aliens probably have received radio signals from Earth for a while, and if they are capable of infiltration, they must have been capable of understanding what was communicated. They would be well aware of Earth’s nuclear capabilities (politicians kept bragging about them, in part to produce a scare in their own populace that would keep them in power, and in part to hopefully keep other nations too scared to attack them), and the then popular concepts of mutually assured destruction and the like. If the aliens consisted of a party of just a couple of thousand individuals, they could just request a bit of land as an autonomous nation, and any bigger nation in the world would gladly grant it to them in exchange for technological advancements. So we know that the aliens need Earth intact, they need Earth NOW, and there’s quite many of them.
All this makes the following scenario likely in my opinion: the aliens have a significantly sized colonization fleet. Maybe their original survey data from Earth is a bit older – if they looked 4000 years ago and happened not to inspect Mesopotamia or China, there is a good chance they figured Earth had no intelligent life. Given how long interstellar travel is likely to take, that is not that absurd a scenario. While approaching our solar system, an initial crew is awoken from cold slumber to assess the situation, make necessary adjustments and prepare Earth for colonization. To their shock they find Earth occupied by militaristic powers with nuclear weapons. If they actually lost their own planet to a conflict between such powers, their threats of total annihilation would seem even more credible to these aliens. The aliens are probably smart enough to realize that a small number of them will be welcomed in exchange for the technology they bring, but a large number would cause concerns and possibly a panic, so they would like to pacify the situation before it escalates. A small number of individuals is sent ahead to take control of Earth’s nuclear assets and ensure safe landing of the colonists. Interestingly enough, the Cold War actually presents a bit of a dilemma to the aliens: if they offer technology to either the US or the USSR, the other might see themselves pushed to initiate aggression out of fear of becoming completely out-teched. As such, interestingly, the aliens would actually want to stabilize and pacify US/USSR relations, trying to come to terms with both of them. At the same time, the aliens want to get in positions of power in the human military, in order to be able to eventually take control of the nuclear weapons. For this purpose, some paranoia between the US and USSR is actually beneficial for them.
Conversely the Xenonauts would want to disrupt the alien infiltration and hinder agreements between the US and USSR that would benefit the aliens. If both the US and the USSR agree to allow a large number of aliens to land and claim territory in for instance both the South American jungles and the Mongolian steppes, the Xenonauts would simply not have the manpower to stop further alien operations.
This also leads to several different end game scenarios:
The aliens took control of Earth’s nuclear arsenal, and colonized the planet. A small number of humans are kept in something similar to zoos for study.
The aliens decided to take the risk, and the humans launched all nukes. Earth is devoid of higher life now.
The Xenonauts were a tad bit too effective in stirring paranoia between the NATO and the Warsaw Pact. Nuclear war erupted between humans, and Earth became uninhabitable.
The Xenonauts managed to foil the infiltration efforts by the aliens, and facing a unified Earth the alien fleet grudgingly turned away in the slim hopes of reaching another colonizeable planet before their resources run out. Humanity is propelled forward in science and technology due to captured alien technology.