President Trump listed eight countries in a new travel ban that he said is intended to protect Americans from harm.

The countries either do not currently manage and screen their citizens to higher U.S. standards imposed since Trump took office, or they present “sufficient risk factors” that require restrictions on their citizens' travel to the United States, the White House said.

The eight nations will remain on the list “until we are sure that we can conduct proper screening and vetting of those countries’ nationals,” the White House said in a statement Sunday night.

Two countries that were on previous versions of Trump’s travel ban were removed from the new one:

Sudan: It is listed as a state sponsor of terrorism and continues to be the site of terrorist activity, yet it was taken off the most recent list of six countries barred. After the U.S. government shared new security requirements with countries in July, some nations agreed to share more information regarding terrorism threats, improved travel document security or did a better job of reporting lost and stolen passports, the White House said.

Iraq: It also has a significant terrorist presence and is still fighting to destroy the remnants of Islamic State fighters within its borders with significant U.S. support. Despite that, travel limitations are not warranted because of the close cooperative relationship between the U.S. government and the democratically elected government of Iraq, the White House said. Iraq had been on the original ban against seven majority-Muslim nations issued in January but was dropped when a revised list of six nations was issued in March.

Here is the situation in each country on the new list and the White House rationale for banning its citizens from entering the U.S.:

Chad

The Saharan African nation has been a U.S. ally in the war against al-Qaeda-linked and Islamic State-affiliated Boko Haram and other radical groups, yet the terrorist threat there has been sufficient to warrant travel advisories by the State Department and Britain’s Foreign Office. “There have been numerous attacks by armed elements in the Lake Chad region throughout 2016 and 2017, where the terrorist group Boko Haram remains active,” the foreign office reported in a recent advisory.

What the White House said: While Chad is an important partner in the fight against terrorists, its government does not share public-safety and terrorism-related information. The order suspends suspended travel for immigrants, business travelers and tourists.

Iran

The Shiite-majority Islamic Republic of Iran is Washington’s primary nemesis in the Middle East. The State Department accuses Iran of supporting the brutal reign of Syrian President Bashar Assad, and terrorist groups and militias in Yemen, Syria, Iraq, Lebanon and the Gaza Strip. Iran also continues to test ballistic missiles, despite a United Nations Security Council resolution forbidding such tests while the 2015 nuclear deal negotiated by President Barack Obama is in force. Trump says Iran’s ballistic missile tests show that it is violating the spirit, if not the letter, of the deal.

What the White House said: Iran “regularly fails to cooperate with the United States Government in identifying security risks,” and that as a state sponsor of terrorism, it is a source of significant terrorist threats. The order suspended travel for all Iranians who are not students or on exchange programs.

Libya

The North African country, whose proven oil reserves rank ninth globally, has been locked in a civil war since the overthrow of strongman Moammar Gadhafi by a U.S.-backed rebel movement in 2011. Warring factions include terrorist militias who fight under the banner of al-Qaeda or the Islamic State, and other militias and armies that control various territories and cities. On Sunday, U.S. Africa Command reported that six airstrikes on Friday killed 17 Islamic State fighters near the Libyan city of Sirte.

What the White House said: While Libya’s government is a terrorist fighting partner, the presence of terrorists and Libya’s “challenges” in sharing public-safety and terrorism-related information was a factor in the decision to ban its citizens from traveling to the U.S. Another factor: Libya has not been “fully cooperative” when it comes to receiving Libyan nationals under orders for removal from the U.S. The order suspends Libyan immigrants, tourists and business travelers.

North Korea

The isolated East Asian nation has been high on Trump’s list of global troublemakers, mainly due to its nuclear weapons program, which has made several breakthrough advances in the past two years. North Korean leader Kim Jong Un has threatened nuclear retaliation if attacked by the United States. This month he tested multiple ballistic missiles with launches that vaulted high over Japan, and a powerful hydrogen bomb for the first time. The U.S. government accuses North Korea of exporting its nuclear technology to Syria, and possibly collaborating with Iran on nuclear and missile technology. North Korean intelligence operatives are suspected in multiple assassinations and in the disappearances of Japanese, South Korean and U.S. citizens in East Asia.

The United States issued 100 visas to North Koreans last year, 52 for business or tourism and the others for diplomats, according a report last month by broadcaster Voice of America. From March to June this year, the U.S. issued 18 visas to North Koreans, according to the report, which said that 1,200 visas were issued a year from 1997 through 2001.

What the White House said: North Korea does not cooperate “in any respect and fails to satisfy all information-sharing requirements.” The suspension applies to all North Korean immigrants and non-immigrant travelers.

Somalia

The East African nation has been in a state of civil war for decades and has an active Islamic State-linked terrorist movement known as al-Shabab. U.S. forces have been working with troops loyal to the government of Somalia, which has expanded its control over the capital Mogadishu, although terrorists have killed dozens of people there this year.

What the White House said: Somalia satisfied minimum U.S. requirements for information sharing, but has significant identity-management deficiencies and is still considered a terrorist haven. The order suspends Somali immigration, and requires enhanced screening and vetting for non-immigrant travelers.

Syria

This war-torn Middle Eastern country that borders NATO ally Turkey, Lebanon, Israel, Jordan and Iraq has been fighting a six-year-long civil war with numerous militias and terrorist groups backed by almost every nation in the region, including Iran and Saudi Arabia, as well as the U.S. and Russia. The Iran-backed Hezbollah militia, al-Qaeda and the Islamic State are all active in Syria, fighting each other. According to the State Department, all three either have attacked or seek to attack Western targets.

What the White House said: Syria’s government is a state-sponsor of terrorism that “regularly fails to cooperate” in identifying security risks, while being a significant source of terrorist threats. The order suspends travel to Syrian immigrants and non-immigrants.

Venezuela

The South American nation has been in turmoil as the anti-American socialist government seeks to quash the political opposition by suspending the opposition-controlled parliament, packing the supreme court with friendly judges and appointing a new elective body of supporters in a referendum condemned by the U.S. government as being rigged. In a speech to the United Nations General Assembly last week, Trump listed Venezuela in a new “list of rogue nations” that updated the “Axis of Evil” coined in 2002 by President George W. Bush.

What the White House said: Venezuela’s government has not cooperated to identify public safety threats, does not share terrorism-related information and has not been fully cooperative in receiving nationals who had been ordered removed from the U.S. The suspension order applies to certain Venezuelan government officials and their immediate family members who are non-immigrants on business or tourist travel to the U.S.

Yemen

The Arabian Peninsula nation has been fighting al-Qaeda terrorists for more than a decade, and is now embroiled in a civil war against Houthi rebels backed by Iran. The shaky government is backed by Saudi Arabia, which leads an Arab coalition in conducting airstrikes in support of Yemeni government forces. Yemen’s military also shares intelligence with the United States, which has fought terrorists there for years.

What the White House said: Although Yemen is an important partner in the fight against terrorism, its government faces significant identity-management challenges, which are amplified by the significant terrorist presence. It also does not share enough terrorism-related information, the White House said. The order suspends travel for Yemeni immigrants and tourist and business travelers.

More:New travel ban adds North Korea, Venezuela

More:Supreme Court: No expansion of travel ban's refugee exemptions

More:President Trump at U.N.: Here are the 3 nations in Trump's new 'Axis of Evil'