BrowserRouter: Real URLs in React SPAs

BrowserRouter turns the address bar into a client-side navigation system, using real URLs without reloads. It is the default choice for SPAs that need shareable links and clean history. Under the hood it uses the HTML5 History API to swap components as the path changes. The footgun is forgetting server-side fallback config: because the browser requests the path from the server on a hard refresh, a missing catch-all rule turns every deep link into a 404.