What’s the point of the Green Belt?

Phineas Harper, writing in ICON magazine, reviews the history and makes the case for green belts around cities. His brief history starts with an idea in 1829 to create 4 concentric circles of urban area and “breathing spaces” around London. Unsurprisingly enough this didn’t happen, but the concept was adapted in new cities in Australia and the USA.
His argument that every urban space needs to have a boundary to prevent urban sprawl, citing the success of three cities that are constrained – Venice, New York and Shibam in the Yemen. He disputes the assertion that the UK green belt drive up the cost of land by arguing that developers, who limit the release of new houses, are themselves limiting supply.
The full article is available  on this link: https://www.iconeye.com/architecture/features/item/13587-every-city-needs-an-ending-the-story-of-the-green-belt