The world's exponential population growth will soon need to flatten out otherwise within a few hundred years every square foot of the Earth's surface will be taken up by a human. (Which reminds me of one of my favorite bumper stickers from a space advocacy group in the 1970s that read: "American Needs Space to Grow.")
With this population growth, mankind's hunger for energy has also increased exponentially. And if this continues, we will soon consume more energy than the Earth receives from the sun. Should they exist, this could be a common problem faced by burgeoning civilizations across the galaxy.
A solution to this energy demand is to become an extra-terrestrial civilization and harvest the resources of a planetary system to colonize space. A daunting yet logical step is to build solar energy-collecting structures in space and live on them.
This concept was taken to its logical extreme by British physicist Freeman Dyson who proposed in 1959 that advanced extraterrestrial civilizations might encase their stars in an artificially constructed sphere, the radius of Earth's orbit.