President Trump on Wednesday signed a travel ban on 12 countries, primarily in Africa and the Middle East, reviving an effort from his first term to prevent large numbers of immigrants and visitors from entering the United States.

Here is a closer look at why the administration says it is instituting full bans on foreign nationals traveling to the U.S. from 12 nations.

U.S. President Donald Trump signed a proclamation on Wednesday banning the citizens of 12 countries from entering the United States, saying the move was needed to protect against "foreign terrorists" and other security threats.