US — United States

The United States is the world's third-largest country by area and population, and the largest economy globally. Washington, D.C. is the federal capital. The US is the birthplace of the internet, Silicon Valley, and much of modern computing. The US Dollar (USD) is the world's primary reserve currency and the de facto currency of international trade. For developers, the US country code and en-US locale are the most commonly used defaults in software development worldwide. The .us ccTLD exists but .com (originally for US commercial entities) is far more prevalent. The +1 dialing code is shared with Canada and several Caribbean nations. US-specific formatting conventions — MM/DD/YYYY dates, imperial measurements, 12-hour time — differ from most of the world and are often hardcoded as defaults rather than treated as locale-specific. The ZIP code system (5-digit and ZIP+4), Social Security Number validation, state/territory system, and multiple time zones create extensive US-specific requirements. The US market's dominance means en-US is often the default locale, but this can create bias in internationally-deployed applications.