The system that took down these "things" was deemed a horrible failure because people were stuck in a ten year bubble like the British government in the 1930s. Until it was almost too late they waited to rebuild their armed forces. They just barely survived because they invested in radar, the Hurricane and the Spitfire and had a bunch of dominions willing to support the mother country (collective security). Strong alliances and strong, confident defense establishments are the only way to prevent WWIII.