The world has changed from a catastrophe that started in the 2000s and that has forever changed how life proceeded. The very earth itself expanded in certain areas the Amazon had an opened portal that was so wide it covered at least 3 million km^2. The other side of that portal was a disgustingly large plane full of ancient civilizations and life of different kinds. Then the Mt Everest had a large portal at the halfway point that opened to a very chilly plane full of very strong beings that were best to be avoided.
The Earth had portals here and there some are being explored while some have been explored like the Palawan portals that opens to a plane of Islands the size of 2 times the Philippines. This has made it so that there were tribes and tribes of different beings. This has allowed the Philippine government to take advantage and conquer said plane. Giving them resources that has changed the magical components of the air with in the Philippine archipelago to being enriched. Therefore, the people became more powerful through the use of magic and has explored the very limit to the current one.
But for greater countries some were lucky while some were not. For example, China had land so wide sometimes a lot of areas are uninhibited by people. A great example would be the Kunlun Mountains spanning kilometers and kilometers making it one of the longest mountain chains on earth. And in these mountains there was a massive portal that spanned around 1000 kilometers wide. The other side was so large that up till now the mountains on the other side were not known if there was a limit to it. Surely that plane would have a limit but so far current human capabilities has not been able to allow humanity to explore it. But just what can be taken from it is already so rich that other countries are green with envy. Such wealth does not come without a cost and the Chinese people were luckily able to cope with what the mountains has currently thrown at it from tribal beings to monster hordes that were seen as catastrophes. They come and go when they like and so the Chinese government has made it so that they would always be prepared for it. Unluckily for them the South China Sea had also opened a very strong portal. These has affected the world badly since the output of China like its exported parts and goods to the rest of the world that has been seen as just whatever are now needed badly.
This has prompted the UN and other affected countries to try and open the silk road through Joint operations. Although successful the cost still affected the prices around the world.
The U.S also had portals but being a country focused on arming themselves they were able to fight them. The most unfortunate of all were the North Koreans the Undead Emperor has chosen it as one his first place to turn into his lands. The land slowly died along with everything in it, It has made it so the element of death is so abundant in it. Some countries has disappeared altogether since they were not able to cope with the portals or the portals were so unfairly strong.
The portals all in all became hotspots for element rich resources and energy which are needed in making the human body progress further. As to what has prompted this catastrophe no one knows as of now.