Two partial timelines have been posted which mostly agree with each other.
1927 - The US Federal Government discovers Deep Ones and hybrids living in the Innsmouth, Massachusetts. They arrest the entire population of the small port town and attempt to cover it up. This attempt fails miserably when pictures of the interred Deep Ones make it into a newspaper. After five years of highly sensational litigation, the population of Innsmouth is released. Most fade into obscurity or return to the Ocean.
September 1937 - France, Britain, and Canada enter World War II.
October 1937 - Several thousand Deep Ones rise up upon the shores of Newfoundland. They immediately march upon the nearest recruiting station and enlist in the Canadian Forces. While Y'ha-nthlei remains officially neutral, over 30,000 Deep Ones serve in the militaries of various Allied powers.
1945 - George Marsh, a Hybrid born in Innsmouth, received the Medal of Honor for valorous service above and beyond the call of duty on the island of Iwo-Jima. He goes on to write a bestselling autobiography detailing his childhood experiences in the interment camps as well as his actions in the Pacific Theater. It's made into a popular motion picture which is eventually remade twice.
November 1963 - Fearing potential nuclear war, Soviet Remote Viewers warn the American Secret Service of an assassination plan by a Communist Sympathizer named Oswald. Oswald is arrested and convicted with little fanfare and spends the next twenty years in prison, where he becomes a Born Again Christian. By the 1990s he's a popular televangelist with a weekly show on CBN.
1967 - The Supreme Court decides Loving v. Virginia, striking down Virginia's anti-miscegenation law and affirming a universal right to marriage.
April 1968 - Outspoken Civil Rights Activist Tlka'nipri is shot by James Earl Ray. He dies of his wounds three days later. Martin Luthor King, Jr. is also hit in the attack, but eventually makes a full recovery.
July 1969 - Apollo 11 Lands on the moon. Neil Armstrong steps out of the lander first and says the immortal unforgettable words, "What the fuck is that thing?" The Moon Beasts feel that the Apolo landing is a violation of their sovereign territory and declare war upon the Earth.
1970-1984: The Earth-Moon War.
The conflict starts off slowly since the Moon Beast space-launch capabilities aren't much better than Earth's. Indeed, Earth pretty much ignores the whole thing for a while. America attempts to negotiate the release of the Astronauts, but no one takes the threat seriously.
On the Moon Beast side of things, the Beasts and their allies, the Men of Leng, staged a major offensive in the Dreamlands, overrunning several Ghoul strongholds and obtaining access to several physical pathways between Earth and the Dreamlands, allowing them to stage assaults on Earth without traveling through intervening space.
Earth's defenders were not prepared to fight an enemy that could move troops through the land of dreams, and several world capitols fell in the initial blitzkrieg, which the Moon Beasts had designed as a decapitation attack. In just a few short weeks Lunar forces controlled DC, Moscow, London, Paris and, Beijing. Able to attack anywhere in the world with little warning, there was no effective defense against them.
Fortunately, though the Dreamland gave the Lunar forces an unmatchable mobility advantage, it was not sufficient to counter Earth's tremendous population and industrial output. Even the use of the Moon-beasts's small nuclear arsenal against major manufacturing centers was insufficient to blunt human industrial output.
A failed assault on Y'ha-nthlei is universally regarded as the worst strategic blunder in the history of interstellar warfare. It brings Dagon himself into the conflict on the side of the Allies. Meanwhile, Ghouls displaced from their dreamland homes by the Lunar army seek refuge amongst the UN forces and teach them how to shift physical matter to the Dreamlands and back again.
In the end the Moon-beast forces are driven back by the might of human industry and are forced to surrender in the face of nuclear annihilation.
A new, permanent, American-Soviet military alliance establishes bases in the Dreamlands and on the Moon.
1992 - Phizer patents Re-Agent, a drug capable of restoring life to dead tissue.
2X97 - The Present.
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1927: Deep Ones discovered in Innsmouth, Massachusetts and become public knowledge after the escape of one of the citizens from the interment camps.
1930: Y'ha-nthlei joins the League of Nations and by 1932 successfully petitions the US government to release the population of Innsmouth.
1937: France, Britain, and Canada enter World War II. Y'ha-nthlei remains neutral along with the US, but 30000 Deep Ones enter into the Canadian and French military forces.
1941: R'lyeh joins the Axis Powers along with Italy, Germany and Japan. Successful joint Japan-R'lyeh invasions of China, Australia, Thailand and Malaya are launched.
1945: George Marsh receives the Medal of Honor. Feature film is made detailing his life. Atomic bombing of Japan occurs.
1952: Major earthquakes felt throughout the United States. Not recognized as early Cthonian weapons testing until mid 1970s.
1963: Soviet Remote Viewers warn the American Secret Service of an assassination plan by a Communist Sympathizer named Oswald.
1967: The Supreme Court decides Loving v. Virginia, striking down Virginia's anti-miscegenation law and affirming a universal right to marriage.
1968: Civil Rights activists Tlka'nipri and Martin Luther King, Jr. are shot by James Earl Ray, with the former dying of his wounds.
1969: Apollo 11 Lands on the moon. Neil Armstrong makes first contact with the Moon Beasts.
1970: First nuclear attacks by Moon Beast forces arrive through the Dreamlands. DC, Moscow, London, Paris and, Beijing, etc, are all hit or captured by Lunar forces.
1971: Soviet forces attempt spavce invasion of the Moon. Landing attempts shot down by Lunar missile defense program.
1972: Edgar Cayce, employed by the US Army, descends the Seven Hundred Steps of Deeper Slumber in hopes of locating a physical entrance into the Dreamlands.
1973: Physical entrance to the Dreamlands located in Nigeria. First United Nations expeditionary force into the Dreamlands is launched, successfully establishing the first Earth beachhead into the Dreamlands. Secondary bases are soon established in Kansas, Siberia, Brazil and beneath the North Sea.
1975: As the Earth-Moon War continues to rage on, Ghoul refugees from the Dreamlands apply for asylum from major earth governments.
1980: Failed invasion of Y'ha-nthlei by the Moon Beasts through the Dreamlands brings Y'ha-nthlei into the conflict.
1983: Operation Moonhammer is launched by the United Nations in December, marking the first Mecha-scale conflict by Earth forces. Dagon rises from the Pacific and flies to the Moon armed with state of the art nuclear weaponry.
1984: Unconditional surrender of last remaining Lunar forces after the atomic bombing of Tycho crater.
1988: Cthonian Earthshaker located in South America and fought using prototype "Gunboy" mecha. Battle is wildly successful.
1992: Phizer patents Re-Agent, a drug capable of restoring life to dead tissue.Cthonian War continues to heat up.
1994: Gunboy MkI mecha goes into full production.
1996: Victory in the First Cthonian War declared by the United Nations after two years of no apparent attacks by Cthon.
2000: Turn of the century sees the arrival of the first Goat Spawn on Earth. After discovering that the Moon Beasts have been defeated, the Goat Spawn announce their presence to the UN and reveal the existence of Shub Niggurath.
2001 to 2031: I have no idea what happens during this period. Maybe this is a good time for Cthulhu to show up. If a third type of mecha needs introduced, this would also be a good time for that.
2032: First Mi Go scouts arrive on Yuggoth using Borean Gate technology. Landings are made in the Arctic using Mi Go spacecraft.
2034: Shudde M'ell awakened by Ithaqua's arrival on Yuggoth, heralding the begining of the Second Cthonian War.
2035: Earth slowly losing the Second Cthonian War as Gunboy mecha prove unable to successfully combat Ithaqua.
2036: Elder Things discovered beneath the Antarctic and revived using a combination of Ghoul science and more advanced versions of the Re-Agent formula.
2038: Ubbo-Sathla captured in Greenland by Union forces along with tablets describing eldritch knowledge.
2040: First prototype of the shoggoth-based "Throne" mecha completed with Elder Thing cooperation. Significant advances made on the Borean Front as a result.
2045: Second Cthonian War ends.
2056: First Youma sightings made in Japan. Affliction is determined to be due to "Black Goat Energy"
2057: Youma agents opens a gate to the Abyss, allowing the second wave of Goat Spawn to begin arriving.
2060: After four years of unsuccessful attempts, the first Youmafication patient to be successfully treated is declared clean of BGE after the Mahou Shoujo Program defeats and captures her.
2065: Earliest members of the Mahou Shoujo Program begin suffering from "Magical Girl Shock Syndrome", resulting in a restructuring of the program toward the current Mentor-Protege relationship.
2076: Last of the second wave of Goat Spawn finally defeated, leading to a generation long respite while Shub Niggurath prepares a new generation of Dark Young.
2077 to 2096: Again, room for stuff to happen here. If Randolf Carter III is doing something, now is a great time.
2097: Today. Third wave of Goat Spawn and Dark Young are expected to arrive any year now, Cthonian sightings are on the increase and the Mi Go are preparing for a second invasion.
I think that most of those concepts are pretty solid. We also want to have a lot of the timeline filled in
even if the "welcome to the 6th world" type chapter at the front doesn't cover every detail right away. Things seem a lot more real if you can make references and allusions to events that you only fully describe later. It's the rpg setting version of foreshadowing. Plus it can make for good plot hooks and inspiration for the GM.
The major sticking point that wasn't quite resolved was exactly how much the water level rises compared to today, and what effect that really happens on the geo-political landscape when combined with the Moon Beast Sneak Attack (which should probably get a cool name to remember it by, like Hydra Strike or something). There's going to be major cities somewhere (even though a lot of stuff is as decentralized as possible to make quick elimination as hard as possible), and where exactly those cities are and what they look like was never really picked out. Frank has written stuff on the 12 Wards, and each Ward should probably have at least one location described enough to use in game (like After Sundown's "___ by night" segments) as well as having a tourist guide type of mention of other places or features within the ward. That all could become very long, but I think that in a game where the setting is very strange it's entirely justified to spend a lot of efforts on working out what that weird thing looks like.