I was doing this in the discussions and decided it might be fun to add to it as movies come out (if I remember and don't lose interest).
Apokolips invaded Earth centuries ago, but humans, Amazons, Atlanteans, the Old Gods, and even protectors from other planets came together to push them back, forcing them to retreat. 
Later the Atlanteans' technological advancements became too much for them to handle and their society was forced underwater, where it remained to the present day. 
Mankind and the Amazons ended up warring, as did the Old Gods amongst themselves. Ares killed each of the Old Gods, one by one, until only Zeus remained. Ares killed him as well, but not before Zeus had a child with the queen of the Amazons and created a divinely-hidden island to which they retreated and continued to live to the present day. 
Queen Hippolyta's half-god daughter, Diana, grew up hearing the legends of the Amazons and gods, and was obsessed with war and protecting Earth from Ares - the Amazons' charge now that the Old Gods were gone. The era of World War I caught up with the Amazons when its soldiers happened upon their hidden shores. Diana left to put an end to it. She sought Ares at the heart of the war only to find that war was simply part of human nature. Ares followed her into the war, and using her newfound view of humanity's rage, tried to convince her to join him in wiping them out. She saw their good as well, and put an end to Ares instead, but also stepped out of the spotlight. As an immortal she lived on through the centuries, helping out with mankind's squabbles here and there, but never fitting in or allowing her actions to take notice from the humans. 
Approaching the present day, the planet Krypton collapsed into itself, wiping out almost the entirety of the Kryptonian people. A family managed to save their infant son by sending him to Earth. He would grow up as a human, but would also be empowered by Earth's rich atmosphere and its sun's radiation, gaining godly powers over mankind, but hiding them unless people needed him. He spent his life looking for his birth parents, until one day finding an ancient scout ship from his home world, sent to explore the universe long ago. Managing to activate the ship, he was able to learn of his origins, but simultaneously the ship signaled out for other Kryptonians, being recognized by the last few remaining in the universe - war criminals who were in an off-world prison during their planet's destruction. These criminals, known as the Sword of Rao, approached Earth to find the signal, and issued a threat to the planet - return the Kryptonian refugee or the world would face the consequences. Zod and his Sword of Rao needed a codex the saved boy, Kal-El, had been given by his parents before his departure from Krypton. Zod planned to use his ship to terraform Earth into a new Krypton, killing all life on the planet, then the data in the codex would enable him to give new life to the Kryptonian people. Kal put on a suit with his family's crest, and stood between humanity and the Sword of Rao, saving the world and becoming known as the hero: Superman. He was forced to kill Zod, while the rest of the Kryptonians had gotten sucked into a singularity triggered by their own powerful technology. 
Not all of humanity saw Superman as their savior, however. Many looked at the carnage of the Sword of Rao's assault and Superman's immense power, and feared him. After all, even though he defeated the Sword of Rao, they came to this world in search of him; he brought them to Earth. Who knows what other horrors he might unleash, intentionally or not. One such man, Lex Luthor, dug deep and discovered Superman's human identity, a number of methods of potentially killing the god among men, and developed a plan to show the world how cruel this god could be - and kill him in the process. Lex manipulated Batman, the vigilante of Gotham City, into viewing Superman as nothing more than an alien threat that needed to be taken down for the sake of the human race. While Lex's plan unfolded, Batman formed his own plan and prepared to either kill Superman or die trying. They fought, and in the midst of fighting, Batman realized Superman had grown up as a human; he had lived a life trying to fit in, forming relationships, and struggling with all the same aspects of human life as anyone else. Batman watched himself become everything he fought so hard against, and joined Superman to put an end to Lex's plan. This was a contingency for which Lex had prepared, and so they were met with a monstrosity created with Zod's body and the Kryptonian technology still available in the scout ship. With Batman's support and the help of the demigod, Diana, Superman was able to defeat the desecration without name, but lost his life in the process. 
Humanity mourned, but they also made plans to fill the void left by the fallen hero. A secret government project called Task Force X was launched, using the most dangerous imprisoned criminals to do some good. Midway City was attacked by a magical being once worshipped as a goddess, and Task Force X was sent in to neutralize the threat. 
Meanwhile, Batman started to develop his own team to protect the world in Superman's absence. And Earth is going to need protecting, as Superman's death awakened ancient Apokoliptian technology left behind all those centuries ago when Earth was invaded. The second wave of Apokolips is coming.