This map shows the Natural Earth Admin 0 - Countries shapefile at 50m resolution. Converted to TopoJSON, only 140K gzipped. Each country is identified by its ISO 3166-1 numeric code.
https://d3js.org/d3.v3.min.js
https://d3js.org/d3.geo.projection.v0.min.js
https://d3js.org/topojson.v1.min.js