Hey readers of Digimon Fusion Kai and YuYuGiDigiMoon. I just create a timeline of YYGDM that I did it for the author (to not waste time and reduce some workload) and with some help. It is pretty diverse consider its like a 'marvel universe', plus I added some minor references and future stories (but not too spoilish). Onto the history.
Disclaimer: Digimon/Sailor Moon/Yugioh/YuYu Hakusho belongs to Toei Animation. Digimon Fusion Kai & YuYuGiDigiMoon belongs to Kanius. Digimon Accel Stream belongs to Chaosblazer.
-100,000 years ago: The Digital World's creation. Ancientmon and Millenniummon once co-exist as the first beings before the respective Light and Darkness of Granasmon and Valmarmon are born. Granasmon and Valmarmon create life of order and chaos, but both gods have different views of rulership, and so a war between light and darkness erupts. Pharaohmon betrays the forces of good, especially Anubismon. Both Granasmon and Valmarmon kill each other. Granasmon's spirit lingers, but Valmarmon's body split himself into 7 pieces while his haunting presence wanders. In the Real World, people will believe that Granasmon and Valmarmon are God and Satan respectively in religion.
-???: The existence of the Makai long before the age of dinosaurs.
-530/418/360 mya: Walking with Monsters (Water Dwellers)
-300/280 mya: Walking with Monsters (Reptile's Beginnings)
-250/248 mya: Walking with Monsters (Clash of Titans)
-220 mya: Walking with Dinosaurs (New Blood)
-152 mya: Walking with Dinosaurs (Time of the Titans)
-149 mya: Walking with Dinosaurs (Cruel Sea)
-145 Mya: The Ballad of Big Al
-127 mya: Walking with Dinosaurs (Giant of the Skies)
-106 mya: Walking with Dinosaurs (Spirits of the Ice Forest)
-65.5 mya: Walking with Dinosaurs (Death of a Dynasty)
-49 mya: Walking with Beasts (New Dawn)
-36 mya: Walking with Beasts (Whale Killer)
-25 mya: Walking with Beasts (Land of Giants)
-3.2 mya: Walking with Beasts (Next of Kin)
-1 mya: Walking with Beasts (Sabre Tooth)
-30,000 BC: Walking with Beasts (Mammoth Journey)
-10,000 BC: The story of Sailors Pluto II and Chaos, daughters of Lord Chronos and Sailor Pluto I. It was how Pluto became her father's successor as a time guardian, while Chaos became the ultimate evil of Sailor Moon.
-8000 BC: Orichalcos corrupted the atlantians, and the Battle of Atlantis took place, resulting Atlantis sunk to the deep seas. The Legendary Dragons and Great Leviathan were sealed. The Legendary Signer, the Crimson Dragon and Signer Dragons battled the Crimson Devil, Red Nova. This resulted in Red Nova being sealed in the Earth, creating the serpent Nazca Line.
-3067 BC: The Scorpion King. After the events of the movie, the title character then leads his forces to try conquered the world (The Mummy Returns).
-3060 BC: The Scorpion King's army was defeated, but Mathayas gave his soul to Anubis to give an army of jackals. The jackal warriors destroy everything in Egypt till they were vanished (The Mummy Returns).
-3000 BC: The Earthbound Immortals disturbed the Inca civilization, the People of the Stars. The Star Dragon King prayed to the Dragon Star for salvation. The Crimson Dragon and Signer Dragons were sent in response. The Crimson Dragon and Signer Dragons battled the Earthbound Immortals, resulting in the Earthbound Immortals and Ancient Fairy Dragon being sealed in the Earth, forming more Nazca Lines.
-1290 BC: High Priest Imhotep engaged in an affair with Anck-su-Namun. Results are not pretty. (The Mummy, The Mummy Returns)
-1009 BC: Reference of Yugioh Forbidden Memories. Dawn of Chaos (Ch. 46-48)
-1000 BC: The events of Atem the Pharaoh, such as him defeating Zorc.
-???: Kaiser Ghidorah and the Rajita once invaded Princess Serenity's realm before they are driven back.
-992 BC: The fall of the Silver Millennium. The Dark Kingdom, led by Queen Beryl and the power of Queen Metallia, invades the Moon Kingdom and the planet Earth. The invasive dark forces destroy much of the royal guard, including Princess Serenity, Prince Endymion, and the Sailor Senshi. Queen Serenity uses Silver Crystal to seal away the invaders for thousands of years and with her last ounce of strength sends her daughter, Endymion, and the Senshi to become reborn as normal humans. Luna and Artemis are also sent with them. Queen Serenity passes away and shatters the Silver Crystal into the seven Rainbow Crystals, each with a Great Youma, who are also reborn as humans as well. At the same time, Ragnarok of Norse Mythology had happen. King Enma refuses to help Princess Serenity and Odin from Beryl and Loki respectively.
-Feudal Japan (1185 1868): The events of Inuyasha. Raizen makes love with Yusuke's ancestral mother, thus receiving the genes of the Mazoku centuries later.
-1400s AD: The spirit of Valmarmon turns Dracula into a vampire and gave him wings.
-1455-1485 AD: War of the Roses (Yugioh The Duelist of the Rose reference.)
-1888 AD: Van Helsing
-1926 AD: The Mummy
-1933 AD: The Mummy Returns
-1946 AD: The Mummy Tomb of the Dragon Emperor
-1950s to 1980s: Forrest Gump
-1980 AD: The Shining. It is revealed that the Overlook Hotel was created by Valmarmon's spirit for luring people to create frightening chaos.
-Between 1980 and 1999 AD: Evil slowly begins to emerge and spread across the world. It takes a while for the first modern day heroes to respond to the darkness.
-1984 AD: Doctor Rob "Dolphin" McCoy begins to experiment in creating artificial life, using drawings made by his son as a basis for the creatures he designs. He is soon joined in his work by students Janyu "Tao" Wong, Goro "Shibumi" Mizuno, Rai "Curly" Aishuwarya, "Babel," and "Daisy" (real names not known). Together, they form the group called the Monster Makers - and create the beings known as Digimon.
-1997 AD: The events of Codename: Sailor V. Minako Aino becomes Sailor V and emerges as Japan's first modern day hero, setting up the rise of heroes' response to the evil forces.' Digimon becomes a children's virtual pet-type computer game, and immediately becomes a big hit.
-1998 AD: Digimon becomes a card game.
-Between 1998 and 1999 AD: Sailor Moon: Classic Super S Story Arcs. The Sailor Senshi are the first group of modern heroes. More heroes will later emerge to follow their example and become allies with them.
-1999 AD: Digimon Adventure (Also an actual TV series)
-2000 AD: The beginning of the 3rd Millennium. Sailor Moon: Sailor Stars Arc. Much later, Cain Bearer's wife, Mei, was killed by the unseen Sailor Chaos.
-Between 2000 AD and 2001 AD: The Japanese government sets up it's own SIGINT organisation to monitor the network, known as "Hypnos." The organization soon becomes aware of the Digimon, existing autonomously within the network, and labels them "Wild Ones," setting up protocols to deal with them as they "Bio-Emerge" into the real world.
-2001 AD: Digimon Tamers. Special Gaiden: Underworld Saga. YuYu Hakusho Manga - Two Shots
-2002 AD: Digimon Zero 02 (Also a TV series). Digimon Frontier. YuYu Hakusho: Spirit Detective Saga. Yugioh: Duelist Kingdom/Battle City.
-March 2003 AD: The Wrath of Pharaohmon/Redux
-Between March and November 2003 AD: YuYu Hakusho: The Dark Tournament Saga. Yugioh: Waking the Dragons/The Grand Prix/Dawn of the Duel.
-November 2003 AD: The Invasion of the Rajita
-Between November and January 2003 AD: Yugioh: Ceremonial Battle
-January 2004 AD: YuYu Hakusho: Chapter Black Saga
-Between 2004 and 2005 AD: YuYu Hakusho: The Three Kings Saga
-July 2005 AD: YuYu Hakusho: The Makai Tournament
-August 2006 AD: Search of the Kuiper Senshi. Digimon Data Squad.
-October 2006 AD: The Taiyoukai Awakening
-2007 AD: Yugioh GX - Year 1
-March 2008 AD of YYGDM-01: Across Dimensions
-Summer 2008 AD: Summer Diaries/Special Edition. Yugioh GX - Year 2.
-March 19th, 2009 AD: Dawn of Chaos. (Ch. 1 Prologue)
-March 25th, 2009 AD: Dawn of Chaos. (Ch. 1 - 4)
-March 26th, 2009 AD: Dawn of Chaos. (Ch. 5 - 8)
-March 27th, 2009 AD: Dawn of Chaos. (Ch. 9 - 27)
-March 28th, 2009 AD: Dawn of Chaos. (Ch. 28 - 40)
-March 29th, 2009 AD: Dawn of Chaos. (Ch. 41 - 54)
-March 30th, 2009 AD: Dawn of Chaos. (Ch. 55, 6th Day)
-March 31st, 2009 AD: Dawn of Chaos. (7th Day)
-Between March 2009 AD: Yugioh GX - Year 3.
-August 2009 AD: Siege of GranDracmon
-March 2010 AD: The Yugioh GX cast (Jaden, Syrus, Alexis, Chazz) graduated.
-May 2009 AD of DF-616: Digimon Fusion Kai Season 3
-April 2010 AD: Neos United/The West Coasters
-2011 AD: Valkyrie Advent
-June 2011 AD of DF-616: Cross Generations (Crimson Digicores Saga/Bebimon Saga)
-December 2011 AD of DF-616: Cross Generations (Curtain Call Episode)
-May 4th, 2012 AD of DF-616: Cross Generations (Super Jax Saga). The Avengers with deviations.
-May 5th, 2012 AD of DF-616: Cross Generations (Shadow Dramon Saga/The Dark Ending)
-December 2012 AD: The Wrath of the Defiants
30th Century: The events of The Rise of Crystal Tokyo. Yugioh 5Ds. The Crystal Age. The Future is Wild of deviations.
That's all for the timeline. A few updates will come if there's any changes.