This interactive tree diagram visualizes the hierarchical structure of world countries, organized by continent and subregion. The visualization uses a horizontal, left-to-right layout to display the hierarchy, with country names rendered as text nodes. The code employs D3 v5's `tree`, `hierarchy`, `linkHorizontal`, and `zoom` APIs to construct and render the SVG graphic. The root node is labeled "World," with branches for continents like Asia, and subsequent subregions like "Southern Asia" or "Western Asia," leading to individual country labels.