The United States could aim to have largest population in the world before the end of the century, thus ensuring its power.

The US now has a population of 316 million - third largest after China, 1.36 billion, and India, 1.28 billion - and could aim for 1.6 billion, simply by opening wide its doors to immigration from across the globe as it did during most of its 237-year history.

If immigration to America were increased to 10 million immigrants per year throughout the remainder of this century, the demographic result would be a US population of about 940 million by 2060 and 1.60 billion by the close the 21stcentury (see Figure 1). The world's second and third largest populations in 2100 are projected to be India, 1.55 billion, and China, 0.94 billion.

However, if in the coming decades America continues with net immigration of about 1.2 million annually, as currently assumed, the US population would reach 420 million by year 2060. Although this projected growth would be an increase of more than 100 million, the US population would fall to fourth place as Nigeria takes over the number three position with a projected population of 460 million in 2060. The populations of the three countries currently larger than Nigeria - Brazil, Indonesia and Pakistan - are expected to peak around midcentury and begin declining thereafter due to projected low fertility rates falling below replacement levels. Also in the longer term, the gap between projected US population, with 1.2 million immigrants annually, versus the larger US population, with 10 million immigrants annually, widens rapidly, resulting in a difference of 1.1 billion Americans at the close of the century.

Immigration is the chief source of America's population growth in the coming decades, unlike China, India and Nigeria. US fertility hovers around the replacement level of about two children per woman and is unlikely to change significantly in the foreseeable future. If immigration were to cease altogether, the US population in 2060 would grow to 355 million, an increase of 39 million, but the labor force would decline by several percentage points and the age structure would be considerably older.

America could easily accommodate a larger population given its considerable size and abundant resources. A population of 1.6 billion would increase the nation's density from today's 33 persons per square kilometers to 165 persons in 2100, about half the level in Massachusetts today. This future density is well below current densities in Germany at 231 per square kilometer; Japan, 335; and the United Kingdom, 255. Even if the world's entire population of 7.1 billion were to reside in America, the nation's resulting density of 732 persons per square kilometer would still be less than current densities of Bahrain, at 1,818; Bangladesh, 1,033; and Singapore, 7,447.

Increased demands for food, housing and energy could be handled with a revitalized US economy and developing underutilized land and natural resources, including natural gas and renewable sources of energy. Innovation and technology could alleviate negative environmental impacts, as has been demonstrated over the nation's two-century history.

Increased immigration is consistent with America's admired tradition of being a nation of immigrants and the eloquent call on the plaque inside the pedestal of the Statue of Liberty: "Give me your tired, your poor, Your huddled masses, yearning to breathe free, The wretched refuse of your teeming shore."

Since the nation's founding in 1776, immigration has accounted for more than half of America's population growth. Without its past immigration waves, America's current population of 316 million would be about 143 million.

Immigrants have shaped American history. At the start of the 20th century, the US proportion of foreign born reached its peak near 15 percent. Considerably higher proportions of foreign born occurred in California, with 25 percent; Massachusetts, 30 percent; Minnesota, 29 percent; and New York, 26 percent. Today, the proportion of foreign born is 13 percent - leading states are California, 27 percent; New York, 22 percent; and New Jersey, 21 percent. Countries with higher proportions of foreign born include Australia, 22 percent; Canada, 21 percent; and Israel, 40 percent.