Basic programming skill is all you need to mine, but doing it well requires lots of electricity, and ASICs, Application Specific Integrated Circuits, specifically designed for bitcoin mining.
Most of it is done in China and Iceland, as China has hydroelectric dams, and Iceland has free magma electricity, and snow to cool their rigs.
The more miners, the rarer the required result, so it definitely gets more difficult, but again, it's not a complex problem, just something you need to do trillions of times a second, to hope to stumble on a sufficiently rare outcome.