### Document: Understanding the Primary Currency Usage of USD and KRW

The primary currency in any nation is a crucial foundation for its economic structure, affecting everything from daily purchases to international trade and monetary policy. In this context, the United States Dollar (USD) and the South Korean Won (KRW) serve as the primary currencies in their respective countries, the United States of America and the Republic of Korea. The usage of these currencies reflects significant aspects of each nation's economic identity, history, and connections to the global market.

### United States Dollar (USD)

#### Overview
The United States Dollar, symbolized as USD and often referred to as the dollar, is the official currency of the United States. It is also widely used as a global reserve currency, held by both individuals and central banks for international transactions and investments. The USD is issued by the Federal Reserve System (the Fed), which acts as the central banking system of the United States.

#### History
The U.S. dollar was adopted as the official currency of the United States by the Coinage Act of 1792 which established the U.S. Mint. Before its establishment, various foreign currencies were used for trade within the newly independent states. The creation of a unified currency was a critical step in unifying the various states economically under a single national framework.

#### Influence
The USD's role extends far beyond American borders. It is a dominant vehicle currency in global trade and is often used as a standard currency in commodities markets, meaning that prices of commodities like oil, gold, and many others are typically denoted in USD. Furthermore, many countries hold large reserves of U.S. dollars, and some nations have even adopted it as an official currency or tether their own currency’s value to the dollar’s stability. 

### South Korean Won (KRW)

#### Overview
The South Korean Won, symbolized as KRW, is the official currency of South Korea. It is issued and managed by the Bank of Korea, South Korea's central bank. The Won is divided into 100 jeon, the subunit of the Won, although the jeon is no longer used for practical currency and only appears in foreign exchange rates.

#### History
The South Korean Won was first issued in 1902, replacing the Korean Yang. It underwent several transformations influenced significantly by the historical and political changes in the region, especially around and after the Korean War. In 1962, the Won was reintroduced as the "new Won", and again in 1983, modern, more secure banknotes were issued to combat counterfeiting.

#### Economic Role
The KRW is predominantly used within South Korea and symbolizes South Korea's economic development and robustness. It is not a major world reserve currency, but it holds a significant place in East Asian financial markets. The valuation of the Won is determined by market forces, and the Bank of Korea plays a central role in maintaining price stability and managing monetary policy within the country.

### Conclusion
Both the USD and KRW serve as primary currencies in their respective nations and embody significant aspects of their national economic profiles. They cater to both domestic needs and fulfill distinct roles in the international financial landscape. Understanding when each currency is used, American travelers or businesses operating in South Korea, and South Korean travelers or businesses operating in the USA, need to be aware of the local currency in order to operate effectively and navigate their transactions smoothly.