President Trump on Saturday ordered 25 percent tariffs on all Mexican exports to the United States and a similar levy on all Canadian goods, except for a 10 percent tariff on Canadian energy. His move sent shock waves through both nations, whose leaders have warned that the tariffs will harm all three countries and disrupt their deeply interwoven economies.

On his first day in office, Mr. Trump had vowed to impose punitive tariffs on Mexican and Canadian exports on Feb. 1, to force the two countries to better secure their borders against the flow of undocumented migrants and drugs.

The tariffs target the United States’ closest neighbors and key trading partners. Mexico became the United States’ largest trading partner last year, exporting a variety of goods, including automobiles and avocados, while Canada is the largest foreign supplier of crude oil to the United States.

Mexican officials have criticized the tariffs, arguing that they will not only harm Mexico’s economy, but will also hurt U.S. companies that have production plants in Mexico, including General Motors and Ford. American consumers are also likely to see higher prices for fruits, vegetables and other products.

President Claudia Sheinbaum of Mexico said on Friday that the country was “prepared for any scenario.” She has suggested that Mexico could retaliate with tariffs of its own.

Here is what to know about the tariffs:

Why is Trump imposing tariffs on Mexico?

Mr. Trump placed Mexico and the U.S. southern border at the center of his presidential campaign, railing against record levels of undocumented immigrants entering the United States, as well as the movement of fentanyl into the country. (Border crossings are currently at significantly lower than the record levels in 2023.)

Mr. Trump accused Mexico of allowing a “mass migration invasion” into the United States, claiming that this had brought “crime, and drugs,” crushed wages and overwhelmed school systems.

It is not the first time Mr. Trump has used tariffs as a strategy to achieve policy objectives involving immigration.

During his first term, he threatened to impose taxes on Mexican products to pressure the country’s president at the time, Andrés Manuel López Obrador, into cracking down on migration.

As a result, Mexico deployed National Guard officers across the country to take on illegal immigration and agreed to the expansion of a program that allowed migrants seeking asylum in the United States to remain in Mexico while their legal cases proceeded.

What has Mexico done to counter the flow of immigrants over the U.S. border?

Mexico has significantly increased immigration enforcement in recent years, particularly during the Biden administration. It has added hundreds of immigration checkpoints across the country, including along once-deserted sections of the border, conducted inspections on commercial bus routes and drastically increased detentions.

To deter people from reaching border cities like Tijuana, a top migrant entry point near San Diego, Mexican authorities raided hotels and safe houses, increased security at official crossings and installed new border checkpoints where migrants were passing through a gap in a wall.

Mexico also moved migrants away from the border, using chartered flights and buses to drop large numbers of people in southern cities like Villahermosa. The strategy contributed to a plunge in apprehensions of people trying to cross along the southern border at the start of last year.

The government also introduced bureaucratic obstacles for migrants trying to make it to the United States. At one point, it stopped issuing documents that allowed migrants and refugees to stay in Mexico.

Karoline Leavitt, the White House press secretary, alluded to these actions this past week when she said the Trump administration had seen “a historic level of cooperation from Mexico” on border security.

What has Mexico done to control the trafficking of fentanyl?

Ms. Sheinbaum has taken a far tougher line than her predecessor in cracking down on the criminal groups involved in the fentanyl trade.

Mr. López Obrador prioritized tackling the social and economic root causes of drug crime over enforcement actions. But during Ms. Sheinbaum’s first four months in office, Mexican security forces have conducted major seizures of fentanyl and stepped up operations to locate and destroy clandestine fentanyl laboratories. Security forces have also targeted key members of the Sinaloa cartel, the powerful criminal organization largely responsible for the fentanyl pouring over the southern border.

In December, Mexican security forces seized more than a ton of fentanyl, the equivalent of more than 20 million doses of fentanyl pills, in what Ms. Sheinbaum described as “the largest mass seizure of fentanyl pills ever made.”

Mexico’s security minister, Omar García Harfuch, announced this past week that since Ms. Sheinbaum took office on Oct. 1, more than 10,000 people had been arrested on serious criminal charges, including homicide. Mexican authorities also have seized 90 tons of drugs, including more than 1.3 tons of fentanyl, and destroyed more than 139 laboratories, Mr. Garcia Harfuch said.

Some of the most decisive efforts to curb rampant violence have focused on the state of Sinaloa, where rival factions of the Sinaloa cartel have turned the state into a war zone after Ismael “El Mayo” Zambada Garcia, a top leader of the cartel, was lured onto a plane under false pretenses and sent to the United States, where he is under indictment.

Though there is no evidence that these enforcement actions have made a significant dent in the Sinaloa cartel’s production abilities, analysts say that it has sent a clear message about Mexico’s commitment to make good on Mr. Trump’s demands.

“There are thousands of clandestine fentanyl kitchens in Sinaloa alone, and the drug is so immensely profitable the cartel is not just going to hand it over to the authorities,” said Eduardo Guerrero, a Mexican security analyst.

“But the important thing was to show that Mexico is working harder and faster and making good in this promise to produce results,” he added.

Mexico has also recently passed a constitutional reform to prohibit the production, distribution and sale of chemical precursors needed to manufacture fentanyl. It has also increased laws around offenses related to fentanyl.

What has Mexico told Mr. Trump about its efforts?

After Mr. Trump’s victory, Ms. Sheinbaum said he should consider what Mexico has done to curb the flow of fentanyl and illegal immigration.

In a letter to Mr. Trump, Ms. Sheinbaum said a “comprehensive” migration policy to care for migrants arriving in Mexico from different countries and seeking to reach the United States had led to a 75 percent drop in encounters along the United States-Mexico border from December 2023 to November 2024.

Half of the migrants who arrived in the United States entered with a legal appointment to claim asylum since the United States introduced an app that allowed migrants to make those appointments, she added. (The Trump administration has shut down the app-based entry program.)

“For these reasons, migrant caravans no longer arrive at the border,” she said.

Ms. Sheinbaum, in the same letter, reiterated Mexico’s “willingness to prevent the fentanyl epidemic” from continuing to take a toll in the United States, and highlighted enforcement actions that resulted in the seizure of tons of synthetic drugs.