Lost in Another World: Return to Earth

In 5201 AD, after thousands of years of environmental management, the earth's environment has returned to a green state, no longer full of polluted gases like in the 21st century; however, scientists from many countries have discovered that this state will not last long, and the earth will be at risk of disintegration in the next few thousand years. Since then, the earth has entered the era of the Grand Alliance, and many countries no longer entangle themselves with their own interests, and have begun to explore the pursuit of human living space...