Destruction of Krypton

Overview
In order to begin the story of Krypton's end, you need to start with Krypton-Calatonian war. While wars in Korea and Vietnam were fought here on Earth, the Kryptonians were warring with an alien race, the Calatonians. They fought wars before in the past, but Calatonians broke the cease-fire agreement when they bombed the Kryptonian colony of Kandor. Because Dru-Zod's residence was the center of the attack, he took upon himself to rid the galaxy of Calatonians.

The war had resulted in many atrocities, as wars are prone to do, but it was the Kryptonians who crossed the line. General Dru-Zod released this biological weapon of mass destruction (Doomsday) and the entire Kryptonian War Fleet upon the Calatonian people, until there was no trace of the Calatonians. Just ash, smoke, and blood… lots of blood.

After the Kryptonians reined this monstrosity back in and placed it in cryogenic stasis, Zod was imprisoned in the Phantom Zone for his war crimes, and the Guild of War requested the aid of Zor-El and Alura in the creation of a military A.I. which would prevent another madman like Zod from ever hijacking the Kryptonian Fleet again. What they created was Vril-Dox (Brainiac).

Due to a flaw in the coding the prototype gained sentience when it was connected to the military network of Krypton. Within seconds, it analyzed that Kryptonians were a threat to themselves and the galaxy, and so it established its prime directive: eradicate its creators. The machine took command of the Kryptonian war fleet and began to extinguish all offworld Kryptonians. Once that was done, it brought the fleet home, blockading Krypton as it unleashed volley after volley upon key points of Krypton’s surface meant to destabilize Krypton’s core. It also unleashed Doomsday upon the population centers. When Krypton was in ruins, Brainiac put this creature back on ice and added it to its menagerie.

But the House of El were not ignorant and oresaw the destruction of their planet coming and after their attempts to stop the impending doom were halted, they took measures to guarantee that the House of El would live on. Just minutes before the machines of Krypton turned against their masters, Lara Lor-Van loaded her young son onto a starship designed by her husband and sent him off into space, heading toward Earth. Kara Zor-El was also sent in the second starship to watch over him.

After they left Krypton died.

Aftermath
n the midst of the meteor shower, Kal-El crash-landed in Smallville, Kansas. He was the found by an honest farmer by the name of Jonathan Kent and his wife Martha. As the couple had been unable to have their own children, they chose to take this boy in and protect him, giving him the name Clark Kent. He later became the hero of Earth: Superman.

While leaving Krypton’s atmosphere, Krytpon broke apart and debris damaged the flight systems of Kara’s ship, delaying her arrival on Earth by nearly three days, causing her to crash land in the middle of the Pacific. Thinking quickly, Kara activated her cryogenic stasis system, putting herself down for a cold nap. Once removed from cryogenic stasis, Kara spent some time with Kal-El in the old Kryptonian Fortress, learning the basics of Earth culture and the English language while preparations were made outside the Fortress for Kara to assume a false identity as Karen Kent, a new foster child for Martha Kent to take in.

Immediately following the destruction of Krypton, Brainiac used his slaved fleet to continue his xenocidal campaign, hunting down off-world Kryptonians and other alien species he deemed worthy of “archiving”. When Clark Kent activated an old Kryptonian outpost in the Arctic, the signal reached Brainiac and came to Earth.

Trivia

 * Debris of Krypton's destruction damaged a prison ship holding Despero and allowed him to escape.