1Fan-favorite creators Kurt Busiek and George Pérez craft a new era for Earth's Mightiest Heroes! The Avengers forge an uneasy alliance with the Thunderbolts to face Count Nefaria - but the true threat comes from the stars as Earth is declared a cosmic maximum-security prison for alien criminals! To save their planet, and to contend with hordes of rampaging Hulks and the spawn of Ultron, the Avengers must rebuild their operation bigger and better than ever. But when the time-spanning Kang the Conqueror wages war on the present day - and wins - Captain America and a small band of rebels may be the world's only hope for freedom! Collecting AVENGERS (1998) #24-56 and #1 1/2, AVENGERS ANNUAL 2000-2001, THUNDERBOLTS (1997) #42-44, MAXIMUM SECURITY: DANGEROUS PLANET (2000), MAXIMUM SECURITY (2000) #1-3, and AVENGERS: THE ULTRON IMPERATIVE (2001).