Overpopulation is part of the problem, as is over consumption. It's not about space. There's plenty of space. The problem is the production of goods and services (buildings, food, cars, electricity, etc) for the population is using up the Earth's finite resources and destroying its biosphere due to pollution and climate warming. The larger the population and the more it consumes, the larger the problem. In the US, we all drive, travel by air, enjoy air conditioning, and consume a lot of everything, so our impact on the environment is much higher than say, India, with a population four times larger, but low rates of consumption. China (27.8%), the US (14.7%), and India (6.8%) lead the world in carbon emissions, and so all three need to clean up their acts.