According to the Environmental Protection Agency, urbanized land in the United States increased by 48% from 1982 to 2003 and now covers more than 100 million acres. This expansion of cities and suburbs has had significant impacts on wildlife through habitat loss, pollution and the introduction of nonnative species.

The United States is a country founded by immigrants, yet immigration has never failed to stir controversy. Much of the discussion centers on illegal immigration, but the number of people who arrive legally and their contributions to the U.S. economy — or their cost — has also elicited debate.

Every summer in the United States, the issue of children being left unattended in motor vehicles hits the headlines. The stories often spur outrage and confusion over how such tragedies continue to occur, despite the media attention and persistent warnings to parents about how closed car windows trap heat, rapidly increasing interior temperatures.

According to recent estimates by the Centers for Disease Control and Prevention (CDC), there are more than one million HIV-positive people in the United States. Deaths associated with AIDS number more than 18,000 a year, while 56,300 new HIV cases are reported annually.