Query: The report […] found that the United States was one of the most pollution-free nations in the world.”

Relevant passages:
Developing country <=SEP=> A developing country , also called a less developed country or an underdeveloped country , is a nation or a sovereign state with a less developed industrial base and a low Human Development Index ( HDI ) relative to other countries . There are no universally agreed-upon criteria for what makes a country developing versus developed and which countries fit these two categories , although there are general reference points such as a nation 's GDP per capita compared with other nations . Also , the general term less-developed country should not be confused with the specific least developed country . The term `` developing '' describes a currently observed situation and not a dynamic or expected direction of progress . Since the late 1990s developing countries tended to demonstrate higher growth rates than the developed ones .   There is criticism for using the term developing country . The term implies inferiority of a developing country or undeveloped country compared with a developed country , which many countries dislike . It assumes a desire to develop along the traditional Western model of economic development which a few countries , such as Cuba and Bhutan , choose not to follow . An alternative measurement that has been suggested is that of gross national happiness . Countries on the boundary between developed and developing are often categorized under the term newly industrialized countries .   According to authors such as Walt Whitman Rostow , developing countries are in transition from traditional lifestyles towards the modern lifestyle which began in the Industrial Revolution in the 18th and 19th centuries .   In the 2016 edition of its World Development Indicators , the World Bank made a decision to no longer distinguish between `` developed '' and `` developing '' countries in the presentation of its data . Nobody has ever agreed on a definition for these terms in the first place .

United States <=SEP=> The United States of America ( USA ) , commonly known as the United States ( U.S. ) or America , is a constitutional federal republic composed of 50 states , a federal district , five major self-governing territories , and various possessions .  Forty-eight of the fifty states and the federal district are contiguous and located in North America between Canada and Mexico . The state of Alaska is in the northwest corner of North America , bordered by Canada to the east and across the Bering Strait from Russia to the west . The state of Hawaii is an archipelago in the mid-Pacific Ocean . The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea . Nine time zones are covered . The geography , climate and wildlife of the country are extremely diverse .   At 3.8 million square miles ( 9.8 million km2 ) and with over 324 million people , the United States is the world 's third - or fourth-largest country by total area , third-largest by land area , and the third-most populous . It is one of the world 's most ethnically diverse and multicultural nations , and is home to the world 's largest immigrant population . The capital is Washington , D.C. , and the largest city is New York City ; nine other major metropolitan areas -- each with at least 4.5 million inhabitants and the largest having more than 13 million people -- are Los Angeles , Chicago , Dallas , Houston , Philadelphia , Miami , Atlanta , Boston , and San Francisco .   Paleo-Indians migrated from Asia to the North American mainland at least 15,000 years ago . European colonization began in the 16th century . The United States emerged from 13 British colonies along the East Coast . Numerous disputes between Great Britain and the colonies following the Seven Years ' War led to the American Revolution , which began in 1775 . On July 4 , 1776 , during the course of the American Revolutionary War , the colonies unanimously adopted the Declaration of Independence . The war ended in 1783 with recognition of the independence of the United States by Great Britain , representing the first successful war of independence against a European power . The current constitution was adopted in 1788 , after the Articles of Confederation , adopted in 1781 , were felt to have provided inadequate federal powers . The first ten amendments , collectively named the Bill of Rights , were ratified in 1791 and designed to guarantee many fundamental civil liberties .   The United States embarked on a vigorous expansion across North America throughout the 19th century , displacing Native American tribes , acquiring new territories , and gradually admitting new states until it spanned the continent by 1848 . During the second half of the 19th century , the American Civil War led to the end of legal slavery in the country . By the end of that century , the United States extended into the Pacific Ocean , and its economy , driven in large part by the Industrial Revolution , began to soar . The Spanish -- American War and confirmed the country 's status as a global military power . The United States emerged from as a global superpower , the first country to develop nuclear weapons , the only country to use them in warfare , and a permanent member of the United Nations Security Council . The end of the Cold War and the dissolution of the Soviet Union in 1991 left the United States as the world 's sole superpower . The U.S. is a founding member of the United Nations , World Bank , International Monetary Fund , Organization of American States ( OAS ) , and other international organizations .   The United States is a highly developed country , with the world 's largest economy by nominal GDP and second-largest economy by PPP . Though its population is only 4.3 % of the world total , Americans hold nearly 40 % of the total wealth in the world . The United States ranks among the highest in several measures of socioeconomic performance , including average wage , human development , per capita GDP , and productivity per person . While the U.S. economy is considered post-industrial , characterized by the dominance of services and knowledge economy , the manufacturing sector remains the second-largest in the world . Accounting for approximately a quarter of global GDP and a third of global military spending , the United States is the world 's foremost economic and military power . The United States is a prominent political and cultural force internationally , and a leader in scientific research and technological innovations .