United States Immigration
One of the most famous facts about the United States of America is that it's an immigrants' country. Today, immigration to the United States. has become controversial but looking at the history of the country, immigration is what made the USA what it is today. The foundations of the USA are based in Europe, Asia and in Africa. There were a few waves of immigration from the old world to the new and naturally, almost all Americans have "foreign" origins.
At the beginning, the USA was a "new world", a place where anyone who believes in hard work will have a chance to fulfill his dream. With the vast unpopulated territories (and some populated ones) and the natural resources, the United States held a promise to anyone from the old world, regardless of race and religion, who wanted a second chance; and in comparison to many places in the world, this American Dream is still far from the state in their home country, throughout the history and even today.
The Statue of Liberty - The American symbol of freedom. Image from Wikimedia (public domain)
History of US immigration
According to Wikipedia the immigration to USA can be viewed in four epochs:"...the colonial period, the mid-nineteenth century, the turn of the twentieth, and post-1965". The history of immigration to USA is discussed thoroughly in Wikipedia.
A chart of the ancestries in the United States - The 2000 census.
USA immigration today
Nowadays, the immigration to the USA is not as flexible or free as it was 100 years ago. Nevertheless, despite tougher border scrutiny and many attempts to decrease these numbers, each year, there are approximately more than 1 million legal immigrants to the USA; and about 1.5 million illegal immigrants.