President Donald Trump's sweeping new travel ban came into effect early Monday immediately after midnight, barring citizens from a dozen nations from entering the United States and reviving a divisive measure from his first term.

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.

The White House’s latest travel ban imposes restrictions on citizens from nineteen countries. Many of those affected are contending with crises at home.