It began during World War 3.
Due to the heavy need for energy and the harsh limitations and danger of relying on Nuclear power, various nations had to change their methods for building power plants to power up their cities and even had to switch to alternate forms of fuel for their war machines.
Geothermal energy became one of the most popular options. Underground power plants were also protected against the most powerful weapons of warfare. Even weapons of mass destruction couldn't penetrate the Earth so easily.
Soon, most nations had changed the way of building objects. It was only the proud nation of Australia who built a towering edifice which became one of the most famous bases as they had the technology to stand firm, immune from most of the destructions that were thrown to them.