How many years has the national history of the United States been?

The history of the United States from 1776 July 4th, the "Continental Army" with George Washington as the commander-in-chief adopted the Declaration of Independence, and officially announced the establishment of the United States of America (although the previous Indians had been living in the American continent, it was not counted as the United States), so it only had a history of more than 230 years. /kloc-At the end of 0/5, Spain, the Netherlands, France and Britain began to immigrate to North America. Britain came from behind, and by 1773, Britain had established 13 colonies. American land was a British colony at the beginning of the founding of the People's Republic of China. However, at that time, it was only the embryonic form of America. In the 100 years after 1776, the territory of the United States almost expanded by 10 times. As an immigrant country, the United States has gathered elites from all over the world. After World War II, the United States became the world's largest economic power with its excellent infrastructure, attracting many multinational companies and financial institutions to set up their headquarters in China. Have the largest capital market in the world; Have developed agricultural and consumer markets; It has a great influence on international financial institutions such as the International Monetary Fund and the World Bank, and the modern market economy is highly developed. It is the world's largest economic power.

The reason why science and technology are so developed is related to the consistent insistence of the US government. The United States has always regarded science and technology expenditure as an investment in the country's future, and formulated science and technology policies on this basis. National defense research and basic research have always been valued. The former is mainly to maintain military superiority, while the latter is based on the consideration that basic research is the foundation of the country's long-term development.