A Key Event

The Cosmos war
The Cosmos war was an event wich collaped the ENTIRE COSMOS into one planet at one point of time

wich means that everything from the entire Cosmos was happening at once on just one planet wich is a very dangerous

and everyone started fighting

Some information might be added here:
-we don't know wich year but after the war was over all of the survivors got frozen and they woke up in the year 2900

-it's almost like a combination of Crisis on infinite Earths and zero hour

-every dimension from the 0th dimension to the 10th dimension also collaped into one dimension (but not the 11th dimension tho because the 11th dimension is beyond the Cosmos)

-The Cosmos war can also just be called "Crisis"

-The Cosmos war theoretically took place between the 3rd and 4th season of the flash

The Cosmos war timeline:
-the year 10,000. in this year everything has been destroyed with only a few survivors, Humanity is the only race that survived.

-The year 105105. another ice age.

-The year 252525. Society started building things again and they actually lived in peace (kinda).

-The year 351120. in this year the whole planet was flooded.

-The year 1,000,000 1/2. Giraffes are the new kings and rulers of the world.

-The year 5,000,000. Humanity has split.

-The year 10,000,000. robots have taken over the planet,

-The year 50,000,000. almost every man on earth has died, in this year humanity has found peace.

-The year 1,000,000,000. The whlole planet died or you could say EVERYTHING died

-The year 10,000,000,000,000,000,000,000,000,000,000,000,000,000. The Cosmos died and nothing exist anymore.

-sometime. A new Cosmos is born by green arrow before he died and now we're in The After Crisis (AC) Timeline

The After Crisis (AC) Timeline
The new Timeline. Earth 1, Earth 2, Earth 3, maybe Earth 19, Earth 38, Earth X, Black lightning's Earth and maybe a lot more Earths have been merged together and made a completely new Timeline