Everyone knows that 90% of the high elf population was essentially wiped out in the Third War, during the Scourge invasion of Quel'Thalas. But there is one glaring plot hole - look at what Arthas did to some of the high elf warriors (such as Koltira) and the rangers (such as Sylvanas and most of her battle sisters), he raised them into undeath to serve him and the Scourge once again.
We all know how massive the Scourge itself was, able to fight both the Alliance and Horde armies at Northrend at the same time, and inflict massive devastation against their forces, so it stands to reason that the Lich King could control hundreds of thousands of individuals. So why didn't Arthas raise most of the slain high elves of Quel'Thalas after the invasion to supplement his forces, using the entire population of an ancient elven kingdom to help destroy his other enemies? Or why didn't Sylvanas do so after she broke free, having only several hundred dark rangers with her joining the Forsaken at best, or even most recently in the Fourth War, as she and her dark rangers were by far outnumbered by the humans of Lordaeron?