Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres (3.85 million square miles), making it the world's second-largest country by total area. Its southern border with the United States, stretching 8,891 kilometres (5,525 mi), is the world's longest bi-national land border. Canada's capital is Ottawa, and its three largest metropolitan areas are Toronto, Montreal, and Vancouver. Various indigenous peoples inhabited what is now Canada for thousands of years before European colonization. Canada is a parliamentary democracy and a constitutional monarchy in the Westminster tradition, with a monarch and a prime minister who serves as the chair of the Cabinet and head of government. The country is a realm within the Commonwealth of Nations, a member of the Francophonie and officially bilingual at the federal level. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Canada's long and complex relationship with the United States has had a significant impact on its economy and culture.