This visualization displays the hierarchical structure of world countries as a tree diagram, using a horizontal layout where each node represents a country, region, or subregion. The visualization uses D3.js v5 with the `d3.tree` layout and `d3.hierarchy` functions to compute node positions and link paths, rendered as SVG with `d3.linkHorizontal`. Font sizes scale inversely with node depth, and zooming is enabled via `d3.zoom` and event transforms. The data is loaded from a JSON file containing nested country groupings.