One of the key aspects of the Modern Age of Comic Books was that it was the beginning of big events. In 1984, Marvel Comics debuted the first large crossover, Secret Wars, a storyline featuring the company's most prolific superheroes, which overlapped into a 12-issue limited series and many monthly comic books. A year later, DC Comics introduced its first large scale crossover, Crisis on Infinite Earths, which had long-term effects on the "DC Universe" continuity. In the early and mid-1990s, big events were regularly published by Marvel and DC, often leading to extra publicity and sales. These events helped fend-off competition from Image Comics, and such events were more likely to become "collector's items." Some events, such as DC's "Zero Hour" and Marvel's "Onslaught saga" spanned a publisher's entire line while others only affected a "family" of interrelated titles. The X-Men and Batman franchises featured crossovers almost annually. Some of the most significant mid-1990s events, such as Spider-Man's "Clone Saga," Batman's "Batman: Knightfall" and particularly, "The Death of Superman" caused dramatic changes to long-running characters and received coverage in the mainstream media. These events led to significant sales boosts and publicity, but many fans began to criticize them as excessive and lacking compelling storytelling. They also complained that monthly series had become inaccessible because one had to follow a number of comics to understand the full storyline. By the end of the 1990s, the number of large crossovers decreased, but they were still launched sporadically. Crisis on Infinite Earths to Countdown Starting in the early 1960s, DC Comics maintained some aspects of its continuity through the use of a multiverse system of parallel Earths. A cosmic event in the 1985 limited series Crisis on Infinite Earths merged all of these realities and their respective characters into one universe, allowing writers to rewrite from scratch such long-running characters as Batman, Superman and Wonder Woman and also as an attempt at simplifying the DC Universe. In some ways, this helped revitalize DC's characters, though some fans debated (and continue to debate) whether such changes were necessary to begin with or truly beneficial. Events such as the deaths of Supergirl and Barry Allen augmented debate with many fans. Since Crisis, the trend of such retconning/revamping of characters' histories has increased in superhero comics, as has such large-scale crossover events. Even DC found cause to revamp its universe again (but on a smaller