East 38
An informal gentleman's agreement exists between the United States and China, the world's two major superpowers, concerning the Long Earth. The Americans and their allies are free to step out in one direction - referred to as Earth West - whilst the Chinese are free to explore and colonise in the opposite direction of the ring of infinite alternate Earths, known as Earth East.
Whilst in the context of the novels the Chinese have moved on from the form of planned state socialism and collectivisation known as communism, many of the old grandiose dreams still persist from communist days. With the imperative to house, feed and offer decent lives to a population now estimated at two billion, the Chinese can't help but tinker with the new worlds. Just as the old Soviet Union and Communist China expended massive resources and manpower to improve on the landscape Nature had given them, the Chinese could not resist some pretty major improvements on their new property.
The Soviet Union made major attempts to divert water into new canals connecting major rivers - for travelling east-west in a country where the rivers all run north-south - and to build hydro electric dams, and even to divert the flow of major rivers to where it was perceived to be needed more. The Chinese followed suit in their own country. The current governments of Russia and newly independent states are still grappling with the unintended ecological consequences, such as the creation of new deserts where once there was farmland, and the "oh crap" realisation that the Aral Sea is now a third of the size it used to be, as the rivers that used to drain there now... don't.
Similarly, the Chinese tried to improve on Nature in a few Earth East worlds. The intention was good. To divert rivers starting in the Himalayas to drain north rather than south, to make the Gobi Desert green. Or better still, to get rid of some of those inconvenient mountains altogether. Quite a lot of nuclear weapons were used to remodel the landscape.
The result is a group of worlds that are now so badly irradiated and inimical to human life that they are unfit for human habitation and will remain so for thousands of years. Some people just cannot be trusted with brand spanking new planets fresh out of the packaging...
It is possible Terry Pratchett is here alluding to Leonard of Quirm and his excited plans to use explosive metal bombs in major civil engineering works, for eg to remove inconveniently located mountains. This is how it would all work out in practice...