Historically, the United Kingdom was the richest country in the world for much of the 19th century, due to its vast colonial empire and its leading role in the Industrial Revolution. However, by the early 20th century, the United States had surpassed the UK and held the title of the richest country for several decades.
In recent years, other countries have challenged the United States' position as the richest country. China has been rapidly growing its economy and has become a major economic power, while countries like Luxembourg, Switzerland, and Singapore have consistently ranked at the top of global wealth rankings based on GDP per capita.
Therefore, it is not accurate to say that the United States has been the richest country for the entire history of its existence. While it has held this distinction for significant periods, other countries have also claimed the title at different points in time.