Why the United States is called a nation of immigrants?

Numerous people from all across the globe look forward to migrating to the United States. Maybe they are looking to enhance their standard of living or lifestyle, or they think the US is better than all other countries to start a new and better life. Some people also believe that US citizens have more freedom of expression and beliefs than all other countries.

Many US citizens are not native residents of this country. The majority of them are migrated from some of the other countries during the era of colonization. 

The United States is a country that is not representing a particular group or community, but it is the collection of diversified ethnic groups.

When people were experiencing starvation and droughts in China, many people from that country started migrating to the US.

To escape the food shortage and in search of a better livelihood, many people came to the US as immigrants. (See Why the United States is called America?)

Various African people wanted to live a better life than what they were living, and escape poverty, and start the new one. They thought that migrating to the US will help to escape all their problems.

Many children or students migrate to the US in search of a better lifestyle, creating ladders of opportunities through excellent education systems leading to better job opportunities. (See Why is the American Flag Red, White, and Blue?)

The US is a kind of country that did not use to impose many restrictions on immigrants. However, if we talk about the current scenario, the US has started imposing many restrictions on immigrants, and it is not that easy to migrate to the US.

According to the United nations 2013 report, it was concluded that US has the world's highest number of immigrants that is 19.8% of the total population in the US are migrated from one or the other country.