A theory of development
Start with the default state of humankind: poverty and insecurity1. In the cities, this means slums: tin-roofed shacks jammed up against one another, sometimes for miles; shit-strewn streets; spaghetti tangles of pirated power or local generators, if any; sardine-packed minibus taxis; unemployment; gangs; hardly any health care.
Things don't seem so bad in rural areas, except you're easily victimized by disease, drought, politics, and, more insidiously, population growth: the land that fed your ancestors enough that they grew and multiplied isn't sufficient to feed your family, because you're more numerous than they were. This would be much less of an issue with better inputs - seeds, fertilizer, etc. - but we're talking subsistence farming here.
Development. Meaning what? Not GDP growth, necessarily. The short version is, things getting better. Real health care. Real education. Work that turns into a job that turns into a career. Things built to a higher standard than "shambles that barely work." Enterprises that pay for themselves and grow without external money.
Development starts with little droplets, scattered around the city. A government ministry. A good school funded with remittance money. A four-star hotel. A port. A power plant. When you pass through the gates and walls around these places - and they will be gated and walled - you immediately get a sense that you're in a better place. Maybe the paint isn't fresh, but at least the trash is collected, and the water runs. Most of the people here are working; they may not be middle-class by Western standards, but they have jobs, plans, prospects. These places are lonely little islands in a vast sea of grinding, hopeless poverty.
Over time, some new droplets appear, and the old ones slowly iterate, improve, rise higher above the sea. (Unless it's a failed state; in which case they sink. Fortunately such are rare.) The little islands become an archipelago. They cluster together like constellations, near tourist attractions, parliaments, hills with fresh air. A few of them may even merge together into a larger island.
And then something else happens, something interesting and surprising; on the outskirts of the city, a much larger island rises. Untrammeled by history and existing claims and buildings, a semi-distant suburb almost invariably becomes the most agreeable and most progressive zone of a developing city. Miraflores in Lima, or Gurgaon in Delhi, or (I understand - haven't been myself) the Lekki Peninsula in Lagos.
Time passes. And then the inner-city islands begin to connect. Channels and corridors development reach out to one another, and form a network. Beijing was like this five years ago, with grand main boulevards but considerably more downscale neighbourhoods and hutongs behind them. (Think also of Baron Haussman's construction of Paris's boulevards.)
From there it's a not-so-simple matter of draining the sea. But the next step, I think, is the building of steps, ramps, and canals, so that those who live in the sea and those who live in the islands can begin to interpenetrate: because up to this stage, one of the hallmarks of almost all development are the walls, gates, and guards meant to keep the poor out. It's not until now that the rich and poor begin to mingle a little. On metro systems that get you there faster than a car will. In shopping areas and movie theatres where anyone and everyone goes. It's a long, slow process; but then, no one ever said that draining the sea would be easy.
1You can argue that external forces eg colonialization/globalization perpetuate this - though recent evidence is pretty strongly against you re the latter - but it's pretty silly to claim, as some do, that they cause it. That may be true in some specific instances, but in general, it's just a basic zero-sum fallacy.