In recent years, people in Myanmar have endured a military coup, civil war, enforced conscription, aerial bombardment and a devastating earthquake. A new hardship landed Thursday morning, as President Trump ordered a sweeping travel ban that included the citizens of Myanmar.

The action is an effort to stop immigration from nations that Mr. Trump deemed to have a “large-scale presence of terrorists,” among other concerns. The travel ban, announced by the president on Wednesday night in Washington, is set to take effect on Monday. It applies to the people of Afghanistan, Myanmar, Chad, the Republic of Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Somalia, Sudan and Yemen.

Many of these countries have been wracked by conflict, while others are ruled by repressive regimes. In both cases, Mr. Trump’s proclamation closes the door on those hoping to flee to the United States to build new lives.

Citizens of seven other countries — Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela — will be barred from entering the United States on tourist and student visas. They also will not be able to settle permanently in the U.S.

“We will not allow people to enter our country who wish to do us harm,” Mr. Trump said in a message on social media.