The history of the USA dates back only to the 15th century. In the 15th century there was no USA at all. The present territory of the USA was divided among some countries. In the 15th — 16th centuries some territory of the USA belonged to Great Britain (northern and western lands); southern parts (California, Florida, New Mexico, Texas) belonged to Spain, then — to Mexico; the central part, the territory was called Louisiana — to France; Alaska was possessed by Russia; some territories remained to be under Indians control.In 18th century there were only thirteen Britain's American colonies and they broke with Great Britain in 1776 and later were recognized as the new nation of the the United States of America, following the Treaty of Paris in 1783. During the 19th"and 20th centuries, 37 new states were added to the original 13 as the nation expanded their frontiers across the North American continent and acquired a number of overseas possessions.There were three most dramatic experiences in the nation's history: the Civil War (1861-1865), the Great Depression of the 1930s and Vietnam War of the 1960s — 70s