This example visualizes the top 10 most populous countries as a pathetic bar chart, displaying horizontal bars without any axes or labels. Using React with hooks, the code loads UN World Population Prospects 2019 data via `d3.csv`, then renders SVG rectangles scaled with `scaleBand` and `scaleLinear`. The chart computes bar widths from each country’s 2020 population and positions them vertically with `yScale`. React’s `useState` and `useEffect` manage the asynchronous data loading, while `ReactDOM.render` mounts the visualization.