On October 19, the U.S. Department of State issued a rare advisory that Americans overseas “exercise increased caution” due to heightened tensions and chances of terrorism around the world, spurred by the Israel-Hamas war. It’s part of a system of travel warnings that’s been around in some form since 1978, designed to help citizens assess how safe a destination might be at a given time.

The current version of the system, which launched in 2018, gives fluid rankings from Level 1 (exercise normal precautions) to Level 4 (do not travel), indicating how risky countries (and in some cases, regions) are for Americans to visit. Rankings are based on factors such as crime rates, civil unrest, and the threat of terrorism. They are meant to give “clear, timely, and reliable information about every country in the world so they can make informed travel decisions,” says a State Department spokesperson.

Not surprisingly, on October 14, the State Department moved Israel and the West Bank to Level 3 (reconsider travel) and Gaza to Level 4.

Here’s how the advisories work and how to use them.

What is a travel advisory?

The U.S. State Department inaugurated the travel advisory system in 1978, initially aiming warnings at airlines and travel companies. The system was scrutinized after the 1988 bombing of a Pan Am flight from London to New York, which exploded over Lockerbie, Scotland, killing all 259 passengers and crew plus 11 people on the ground.

Investigations found U.S. authorities had been aware of a credible threat to a Pan Am flight but hadn’t informed the public. In response, the media and consular offices began issuing travel warnings. In 2018 the U.S. introduced its current four-tier advisory system. There are near-identical versions in Canada, Australia, and New Zealand.

To determine rankings, the State Department considers a nation’s political volatility, crime trends, medical care standards, and the threat of kidnappings or terrorism. (Politics also ends up playing an unspoken role.) Some countries, such as Russia, receive a Level 4 ranking partly because the U.S. government may have limited ability to assist citizens there. Others rise to Level 4 due to a crisis, such as the military coup that recently rocked Niger.

When the travel advisory system relaunched in 2018, it also included state-by-state evaluations for Mexico, which draws more than 11 million American travelers a year. “Some Mexican states are quite safe for U.S. tourists, while others are riskier due to narco-trafficking violence,” says Ryan Larsen, executive director of the Institute for Global Engagement at Western Washington University. Yucatán and Campeche states are currently at Level 1, while six other Mexican states are at Level 4, including Sinaloa.

(Solo female travelers share tips for staying safe on the road.)

Epidemics and natural disasters also can prompt a travel advisory number to rise. Americans may be prompted to reconsider visiting a country recovering from a tsunami or major wildfires, since their presence could hinder rehabilitation efforts. This occurred after the February 2023 earthquakes in Turkey. Such advisories can remain in place for weeks or months.

The strictest-ever advisories came in April 2021, amid the COVID-19 pandemic, says Larsen, who did a thesis on U.S. travel warnings. At that time, about 80 percent of the world’s countries were at Level 4.

At press time, about 70 percent of the world’s countries were rated Level 1 or Level 2 by the State Department, indicating they’re relatively safe. There are currently 21 countries at Level 3 and 21 at Level 4.

How to use travel advisories

Before booking an international trip, consult the State Department website to see where your destination ranks. While Level 1 and 2 countries are considered relatively safe, you should still register with the U.S. Smart Traveler Enrollment Program (STEP). This lets Americans overseas use their smartphone to receive travel advisory updates and alerts about emerging dangers in their destination (protests, extreme weather).

Level 3 countries are considered more dangerous for foreign visitors, who should “reconsider travel,” according to the State Department. If you are headed to a Level 3 country, which currently includes Pakistan and Colombia, do wider research on its safety and on the places you’ll visit there, advises Jun Wen, a professor of tourism at Australia’s Edith Cowan University. For instance, while some remote areas in the Colombian Amazon still suffer from drug-related violence, cities such as Cartagena and Medellín are relatively safe. Going on a fully guided group or individual tour can also help you navigate destinations where political unrest or crime might impact your safety.

Travelers should study not only the advisories provided by their own country, but also by the U.S., United Kingdom, and Australia to broaden their understanding of the risks in Level 3 countries, Wen says. As for Level 4 countries, that “Do Not Travel” advice couldn’t be any clearer.

Other countries also issue warnings to their citizens about visiting the U.S. Canada recently informed its LGBTQ travelers they may be affected by laws in certain U.S. states. Australia, meanwhile, cautions its citizens visiting the U.S. to be wary of higher crime rates and gun violence, and even to learn safety strategies for active shooter scenarios.

People who visit countries with Level 3 or Level 4 travel advisories don’t just risk their safety. They also may have travel insurance complications, says Linchi Kwok, tourism management professor at California State Polytechnic University Pomona.

(How travel insurance can—and can’t—help when your plans change.)

They must pay much higher premiums, and their insurance can be invalidated if the advisory for their destination is elevated. “Medical coverage can be minimal, too, particularly if the travel advisory is put up against a disease or an outbreak,” says Kwok. “I encourage Americans to think twice before they travel to Level 3 and especially Level 4 destinations.”

Warnings and their impact on tourism

Travel advisories can be biased, Larsen argues. His research found that, while the U.S. didn’t often overstate the risk of travel to countries with which it had poor relations, it did often understate the danger of visiting nations that were its close allies. Elevating a travel advisory can stoke diplomatic tensions between two countries. Once a country is raised to Level 3 or 4, many tourists will avoid visiting, and many American universities won’t let students join study abroad programs.

The economic ramifications of a level change impact individual businesses such as hotels, restaurants, and travel agencies. For instance, J² adventures, a Jewish-focused tour company, saw most of its fall group trips to Israel canceled after the start of the Israel-Hamas war (and the higher advisory level), says cofounder Guy Millo. “This is not just because of the violence on the ground, but because of practical considerations like accessibility of commercial airline flights,” he says. “Most tourists from North America and places around the globe simply couldn’t get here even if they wanted to.”