Marvel's Avengers: Age of Ultron is infamous for its destruction of the fictional nation of Sokovia. The film's devastating climax saw Sokovia helplessly lifted into the sky before it was shattered to pieces and the Avengers tried to save its inhabitants. Of course, this wasn't the first time that Ultron destroyed an entire country.
In Avengers #19-22, by Kurt Busiek and George Perez, Ultron pursued his ongoing agenda against humanity in the "Ultron Unlimited" storyline. The mad robot kidnapped Hank Pym, the Wasp, Vision, Scarlet Witch, Wonder Man and the Grim Reaper. Each of these characters were related to Ultron in some way. While Ultron wanted to wipe out humankind and begin anew, he still held a deep fondness for his "family." To solve this dilemma, Ultron planned to program his robotic offspring with the brain patterns of each of his "family members." Each new being would receive a different combination of these various brain patterns, becoming a unique individual. Using the technology of Pym's Ant-Man helmet to communicate with others, Ultron would then become the hive-master of his brave new world.
In order to create this new world, Ultron needed a starting point. While the Avengers were distracted by Alkhema, one of Ultron's brides, Ultron himself laid waste to Slorenia. Indeed, Ultron sent an army of robots to fire lasers upon the nation, killing countless people and destroying entire villages. Slorenia's seaports, airfields, train stations and railyards were annihilated to keep everyone contained. The military was easily crushed, along with some experimental zombie troops, a cyborg mercenary named Black Brigade and Ember, a folkloric defender of the Dudak minority. Ultimately, everyone in Slorenia was killed within three hours. Ultron claimed Slorenia as the birthplace of his new world, plotting to use their chemical weapons to wipe out the rest of humankind. Slorenia's citizens were also rebuilt and reprogrammed into zombified cyborgs that served his will.
United Nations troops were sent in to combat this threat, but they were no match for Ultron's forces. The Avengers quickly came to rescue their teammates and avenge the people of Slorenia. Earth's Mightiest Heroes went all-out to defeat Ultron, barely managing to destroy the robot. Yet the Avengers soon discovered that this was only one of the hundreds of Ultron's new bodies, which soon had them surrounded. While they put up a valiant fight, the Avengers knew that sooner or later, this army of Ultrons would overwhelm them. Fortunately, the Vision managed to break free of his imprisonment, freeing his fellow captives as well. A pitched battle against the main Ultron ensued. Shortly thereafter, Justice arrived with Antarctic vibranium, an anti-metal that could destroy any type of metal, even adamantium. Hank Pym then used the anti-metal to destroy Ultron once and for all, winning the day.
This Slorenian plot heavily influenced Age of Ultron. Both the film and the comics saw Ultron take control of an entire city, which he would use to begin his next stage of evolution. In the comics, Ultron wanted to destroy humanity with Slorenia's chemical weapons and start over. Similarly, in the MCU, Ultron was going to cause an extinction-level event by sending Sokovia crashing down to Earth, wiping out the human race with its new vibranium core. Both of these plots resulted in a climactic battle against the Avengers, where Earth's Mightiest Heroes took on an army of robots. Additionally, both the comics and the film included the Vision's attempts to change Ultron's mind. Indeed, the Vision appealed to Ultron's sense of love in the comics, just as he lectured Ultron on humanity's virtues in Age of Ultron.
There are a couple of major differences between the comics and the film, however. For instance, in "Ultron Unlimited," Ultron retained an attachment to his "family," basing his new world on his loved ones' brain patterns. Age of Ultron, however, only showed Ultron's fondness of the Vision, rather than an entire makeshift family. "Ultron Unlimited" also saw the deaths of every Slorenian citizen, while Age of Ultron featured the Avengers safely evacuating Sokovia's people. Despite their differences, without "Ultron Unlimited," Age of Ultron would have had a fairly different storyline.