Long before modern borders existed, people used flags as practical signals. In battle, cloth standards helped troops find their unit in the confusion; at sea, banners allowed crews to recognize friendly ships from far away. As trade and state structures grew, those simple markers moved into public life. By the 18th and 19th centuries, as central governments and international ports became more prevalent, many countries adopted a single flag to represent themselves at embassies, official buildings, and civic events. Over time, those flags took on extra meaning — colors tied to movements, symbols from religion or history, and design choices that made each one easy to recognize.
When you put hundreds of flags on one map, clusters emerge almost automatically. Some regions seem to prefer the same colors or layouts; others deliberately use different symbols so they stand apart. Here is an interesting map created by elordenmundial.com that shows these similarities.
The cross used across northern Europe spread with cultural and political ties and shows up in several national flags. In West Africa, many flags use red, yellow and green because those colors were adopted by early independence movements and then became standard choices for new national banners. In the Pacific, a small number of flags still include the Union Jack; that element remains as a visible trace of historic ties to Britain and because some nations chose to keep that reference.
