Any extraterrestrial contact requires a motive. Sadly, most of the motives given in Sci-Fi films are nonsense.
Terran resources - There are no minerals or elements on Earth that could not be found easier or cheaper and in greater quantities elsewhere in the universe. Recently there was even a finding that reported that there was more total water on the Jovian moon Europa than on the surface of Earth. To look back in time, the Ancient Alien proponents' idea that the Annunaki came to Ancient Earth to mine gold is preposterous. There is more gold in Near Earth Asteroids, and likely much easier for an advanced alien race to mine, rather than landing on Earth and dealing with the bronze age indigenous population. And if you had to go to a planet, Mercury might have a higher amount of gold and heavy elements. So water or mineral prospecting is no reason to visit Earth.
Curiosity - It killed the cat, and it can always be a plausible reason for anyone to explore the unknown. But curiosity doesn't have to lend itself only to an aggressive inquiry. For all the non Alien Invasion or First contact stories, curiosity can be reason for any advanced species to visit. There are some who argue that any advanced species would be so beyond us, they wouldn't want to even bother stoping to look at us. We would be as insignificant to them as insects are to us. What you never hear is the reaction from Entomologists who have just had their profession trounced by so called experts. Talk to someone who studies the insect world and revel at the amount of time humans have studies beehives, ant colonies and spider families. If aliens are as obsessed about learning as we are, any advanced alien species could Not avoid a visit to our planet. Any alien intelligence would at least want to note our development and our social customs. If there is information, there is someone who wants to record it. We might seem insignificant to them, but they might still be fascinated by us. Especially if you consider how rare life in the universe might be. Humans would go to great lengths just to find pond scum anywhere in the galaxy, to claim E.T's wouldn't stop to log biological existence is a little short sighted. Still, this isn't enough of a reason to violently invade a planet.
Habitable Biosphere - The Earth is a shining blue lifeboat in space. If an alien species were to invade, simply having a rare and sustainable environment would be a very legitimate motive. Who knows what condition an alien home world would be in once that species has mastered interstellar travel. Over population, pollution and an environmental disaster might drive a species to become desperate to find a new home. Of course, all of this is assuming an alien species would need the exact same atmosphere and climate that we have on Earth. But even if we were close enough, perhaps Earth could be terraformed to conform to the Alien invaders, but who knows if we could adapt to that new environment. If we could live side by side breathing the same air, perhaps it would be more a matter of interspecies cohabitation. But, if our air is poison to a desperate alien, and vice versa, then we might be be up for the fight of our life.
And here is the real point to this post. What could we possibly do to repel an invasion by an highly advanced Alien invader? Really, there is no way humanity at this stage of technical development could repel an force of advanced, interstellar traveling, extra terrestrials; at least, not alone.
Not only is this a reaction to Alien Invasion films, but also a reaction to the reaction to films like Avatar. While the huge grossing James Cameron film may not be the most original work of cinema ever, it is a rather, plot hole free, story. Sure, Unobtainium messes a little with my previous motive argument, but that plot point aside. There are groups who are upset by Avatar, and also films like Dances with wolves and Pocahontas over racist ideas. I can understand how taking an indigenous people of color and having some Caucasian character come off as their White Savior could be insulting. The problem with this is those who are insulted are missing the point. This is not a color issue or even about culture, it is a matter of technological advancement only. If a more advanced culture tries to conquer a less advanced culture, They Will Win. Yes, there is a bloody insurgency that is possible, and there are guerrilla tactics to be a thorn in the side of your occupiers. All of these are only possible if the apposing force is only slightly more advanced. A species capable of interstellar travel, compared to us, is 10 times more advanced than the Spanish who trounced the Incas in the 1600's.
People will get upset between comparisons between Native American peoples and any less technologically advanced tribal culture in fiction, but remember the focus is not on the culture here. This article is simply about Technology. One of the reasons the Indigenous Americans had as many victories as they did was, they adopted the same firearms used by the Europeans. The Native Americans didn't even have Iron Age technology before the European settlers arrived. Racism and Cultural insensitivity can't be the issue when the only topic of discussion is a groups level of technology. Those other factors do matter in other ways, but not when cold technological development is the topic. Certainly, the tribal culture of the Na'vi was heavily influence by Native American history, but while perhaps naive, was still a reverential influence; not a satire or mockery.
So, to put this Humans fighting off Alien invader on its head, a new plot needs to unfold. The Alien Invasion special effects extravaganza must have a third party. While I have my own screenplay I should be working on, the idea is in the Aether now, I might as well put out the idea for others to pick up too.
Earth is approached by an armada of Alien ships. The first scouting missions of the Alien force quickly crush any retaliation. Only a few small battles are lost, and the aliens are clearly only analyzing Earths strengths and weaknesses before a full on invasion. Suddenly a few new ships are seen, with different designs and markings. These ships do not attack, but observe. Through out the corse of the story First Contact takes place between humans and this second alien species. Humans join with this third party to defend Earth from conquest. In the end a new alliance is formed, and the human race is once again safe. The key to it all, Humans would need an ally to fight off a technologically superior alien force. It would not be insulting to humans, to need help, it would just be the reality of technology in warfare.
If I were a more avid reader, I could list the dozens of novels, probably going back to the 1950's that cover this exact idea. Sadly, I don't know a story right off hand that has this plot, but I am sure they exist.
Thus begins the first of many Summer blockbusters, and one of the most special effects-tastic and profitable movie franchises.
