This example shows the hierarchical structure of world countries arranged as a tree diagram, with each country nested under its region and subregion. The visualization uses D3.js v5’s `tree` layout and `hierarchy` function to compute node positions, while `linkHorizontal` generates the curved connector paths between parent and child nodes. The data is loaded asynchronously from a local JSON file via `d3.json`, and the final SVG is sized to fill the browser viewport, rendering all nodes and links without interactive features.