I think that space is so huge and harsh that it's unlikely that any aliens (in the incredibly unlikely event that they find us at all) will bring any kind of weapon of mass destruction or invasion force or anything capable of wiping out humanity all the way across from wherever they are. Unless they were on some kind of religious crusade...
God how I hate religion.
(See what I did therecheesygrin)
Actually, based on humanities own exponential developement, even if the chance of sentient life emerging is pretty tiny, any galaxy, even universe would pretty quickly fill up to the brim with massive space born civilisations. Many scientists have asked in light of this- why don't we meet any aliens or see any evidence of them when their should be multitudes of them filling up the galaxy?
The most likely answer to this is that at some point in every cycle of life in the galaxy/universe one civilisation out of the multitudes inevitably decides to build an automated device to destroy any civilisations or life it encounters to prevent any threats to the civilisation emerging. These are called Von Neumann probes and are logically a very likely prospect that explains our lack of alien encounters- all of the many civilisations that rise up are eventually eradicated by automated probes which prevent the galaxy from filling up.
Also, mere distance is overcomeable by technology- Fusion or Anti-matter power sources are generally believed to be sufficient to enable interstellar travel in a reasonable amount of time. It is just a case of statistics- does your civilisation reach the requisite level of technology without suffering extinction or exhausting the finite resources of its home through excessive waste (I.e humans, it is theoretically possible that by using up all of the oil, we have squandered our chances of having a suitable energy/technology base to develop the technology to leave our solar system)
On a final note, there are very few reasons for aliens to visit earth-
-Resources- Why come to earth? Most elements can be found throughout the galaxy. Just stop of at any solar system to mine.
-Trade- again, why? The technology and resources for space travel means the alien race definatly does not need anything from us that they cannot get from uninhabited rocks nearer to their homes or from other interstellar civilisations.
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Threat elimination- This is one of the most likely. Any civilisation that wants to preserve itself long into the future would likely seek to identify any threats out there and eliminate them before they can become a problem. Most likely to be used for this would be the automated von neuman probes mentioned earlier.
-Habitation- This is another likely scenario. Assuming convergent evolution, or at least that other life prefers planets with land and oceans and an atmosphere to dead rocks and gas giants, then earth is a pretty valuable and rare world- we have yet to identify another like earth, so habitable worlds would be a vary valuable commodity. Of course the problem is removing the humans who would be unlikely to be willing to share earth and who use up so much space and resources.
-Curiosity- This is semi-likely- Scientists do like to study things, but this would likely not involve large scale stuff, as studying us would not likely justify large amounts of expenditure over more tangible benefits.
-Beliefs/Ideals/Religion/Etc- Any culture does have its various beliefs and values. An alien race may believe that some holy being wants them to come to earth for some reason, or an alien race could find our existence to be offensive, which would warrant a pretty hostile venture to earth. Or they could believe that it is a good idea to come to earth and paint all of the left handed people yellow. You can never really know with minds that have nothing in common with ours.
One big thing to watch out for would be significant events in our science that are easily detectable- Our explosions of atomic bombs was one, us putting out radio signals is another. In future us achieving interstellar travel or creating an antimatter annihilation could be other things to get us noticed. Alien civilisations could potentially watch for signs that another civilisation has hit a certain point in its progress- once you have split the atom or created antimatter for example, could mean you are a potential threat. Of course, if I was an alien race watching earth, I would wait to see if humanity burns itself out before acting- Why wipe us out when we can do it ourselves?
Anyways, apart from my rambling- I personally do not think communism is an achievable system in the modern world. For one thing, no one has adequately explained to me how you would move into such a system, or the mechanics of socialism/communism- If all of the people own everything, then how do the people decide what to do with everything? Do they take a vote? Would it not then be more efficient to elect certain representatives instead of the entire nation taking a vote for every little thing? Isn't that what democracy is anyway?
Of course, in communism it is the state that actually owns everything, not the "people". Personally I think "the people" is to much of an abstract term.
In the end, I actually honestly think a far better system would be for everyone to just submit to me in a dictatorship. A dictatorship would actually work pretty well so long as you have a reasonable, rational person (such as myself) as the dictator, and so long as enough people did their part to carry out the dictator's orders.
So come on, pick up your weapon of choice (grassroots action, social media, hacking skills, ak-47s, mind altering substances) and help me to become your lord and master.