It is ironic and yet totally appropriate that the granddaddy of all alien invasion stories remains the most realistic of them all in that humanity is saved because the Martians have no immunity against our diseases. While that simply explanation may or may not explain what happened to the dinosaurs we do know that the arrival of Europeans in the New World introduced small pox and other diseases which decimated the Native American populations, primarily in the eastern part of the continent. However biological truth only gets in the way of good science fiction so that alien encounters in the worlds of "Star Trek" and "Farscape" rarely worry about speaking the local language or breathing the local air, let alone falling prey to the local diseases.
Written by H.G. Wells in 1898, "The War of the Worlds" also has arguably the most famous opening line in science fiction history, although I am sure most of us always hear the voice of Orson Welles intoning the words, "No one would have believed in the last years of the nineteenth century that this world was being watched keenly and closely by intelligences greater than man's" (my second choice would probably be "Billy Pilgrim has become unstuck in time" as long as we are on that topic). The other major contribution to the alien invasion genre Wells provides is the idea that these strange visitors from another planet come because it is Earth that has something special that they need; in this case it is the delicacy of human blood, sucked from living beings (which begs the question, did the Martians know we were such tasty treats or did they just luck out by traveling to their closest neighbor in the solar system?).
Isaac Asimov argued that "The War of the Worlds" could be read as an argument against British colonialism as the empire expanded to the point where the sun never set upon it. By the end of the 19th-century the British Empire covered a quarter of the land area and the population of the world, and while this is an intriguing parallel it does not strike me as being particularly profitable since the analogy is rather subtle and I would think most of his British readers would have entirely missed the point. Given the omnipresent idea of futurism in Wells' writing it is more worthwhile to look at the issues of mortality, humanity's place in the natural order, and the potential evils of technology.
While rereading "The War of the Worlds" to consider it for a Science Fiction class completely devoted to novels about the Red Planet, I was rather surprised to rediscover that it is a good yarn. The fact that his stories hold up, not just as escapist fantasies or scientific romances but as stories that continue to be relevant critiques of both the time in which he wrote and the times in which we live, only serves to confirm the place of H.G. Wells as not just one of the greatest names in science fiction, but also as a social critics and visionary futurist.