This stacked bar chart displays the religious composition of populations across 15 countries, with each bar segment representing a religion's population in thousands. Clicking a bar segment highlights the entire country's bar with a black outline. The React app loads data from a CSV, processes it into a wide format using d3.group and d3.stack, then renders SVG rectangles scaled by d3.scaleBand and d3.scaleLinear, with axes generated by d3.axisBottom and d3.axisLeft.