Once again, a humanitarian crisis is engulfing our southern border, as tens and potentially hundreds of thousands of migrants arrive from Mexico, Central America and around the world in the hope that the Biden administration will let them in and let them stay.

The new administration has certainly given them — and the human smugglers who profit from their journeys — a basis for such hope: The administration declared that it would stop most deportations (a decision since blocked by a federal court), halted construction of the border wall, announced new "priorities" that sharply limit immigration enforcement, stopped expelling unaccompanied minors under health-related authority invoked during the pandemic and began to phase out the Migrant Protection Protocols that helped prevent abuse of our asylum system and end the last surge of family units across the border.

As the most recent U.S. ambassador to Mexico, I am not at all surprised by the border surge: It is a reprise of the humanitarian crisis that engulfed the border shortly after President Andrés Manuel López Obrador took office in Mexico in December 2018. His administration also came into office pledging to adopt a more "humane" approach toward migration and wound up unleashing an inhumane situation at the border. It was only after President Donald Trump threatened to impose tariffs on cross-border trade that the Mexican government reversed course, and from then on the two countries cooperated closely to reduce the flows of third-country migrants across Mexico.

But the biggest factor driving such flows has gone largely unaddressed: the willingness and ability of American employers to hire untold millions of unauthorized immigrants. The vast majority of the people are coming here for the same reason people have always come here: to work (or to join their families who are here to work).

Unless there is a serious effort, through mandatory E-Verify and other relatively simple means, to ensure that persons hired to work in the U.S. are eligible to do so, our country will continue to entice unauthorized immigrants and reward unauthorized immigration.

Would-be migrants, like other people, are economically rational: They weigh the benefits of living and working in the U.S. against the costs and odds of successfully making the dangerous journey across Mexico and into our country. As we have witnessed, shifts in enforcement policy by Mexico or the U.S. that alter the journey's likelihood of success greatly influence migrant flows.

This is a domestic matter that fell outside my jurisdiction as ambassador. But it was certainly awkward for me to ask my Mexican counterparts to crack down on unauthorized migrant flows when our own government had not meaningfully addressed the major engine of such flows. Congress, regardless of the party in control, has never taken the simple step of making E-Verify mandatory for all employers. Nor has the federal bureaucracy — again, regardless of which party controls the executive branch — shown much zeal for enforcing the law against employers. The Department of Homeland Security points the finger at the Department of Justice, while the Department of Justice points the finger at the Department of Homeland Security.

Until we meaningfully hold employers accountable for the people they hire, and disincentivize them from hiring unauthorized immigrants, I am not optimistic about our ability to contain unauthorized immigration.

It is no answer for employers to argue that there are certain jobs that citizens or legal residents will not do. If raising wages will not do the trick, and we really do need immigrants to perform these jobs, then such workers should be brought in legally with work permits and be subject to the full protection of our laws. There are programs in place to do just that, like the H-2A and H-2B visa programs, which permit employers to hire foreign workers to perform temporary agricultural and nonagricultural services or labor in the U.S. on a one-time, seasonal, peak load or intermittent basis.

But here again, the incentives are all wrong. Those programs are cumbersome, and many employers apparently prefer to hire unauthorized immigrants than go to the trouble of hiring eligible legal workers. Employers who do the right thing are thereby placed at a competitive disadvantage.

It is discouraging to see the Biden administration characterizing the "root causes" of unauthorized immigration as poverty, corruption and violence in Mexico, Central America and elsewhere and vowing to address the issue by attacking these problems. These are certainly "push" factors, but they are nowhere near as powerful as the "pull" factor of jobs in the U.S. readily available at wages unimaginable in these other parts of the world.

And obviously the U.S. government has far greater power to regulate the conduct of employers within its own borders than to solve deep-rooted social problems abroad. Indeed, the U.S. has been talking about improving conditions in Latin America for more than half a century, with precious little to show for it.

As long as our country continues to incentivize unauthorized immigration by turning a blind eye to the employment of millions of unauthorized immigrants within our borders, we cannot claim to have a "humane" policy. Such migration is big business for criminals; it encourages impoverished people to turn over their life savings to the human smugglers who control the routes. The transportation is hellish. Migrants find themselves jammed into locked, and sometimes abandoned, tractor-trailers like those recently discovered in Mexico's Veracruz State with up to 233 people aboard. Last month, 13 people died when an eight-passenger SUV packed with 25 unauthorized immigrants collided with a big rig just over the border in California. Migrants are routinely subject to rape, assault and other crimes. And unauthorized immigrants who ultimately succeed in reaching our territory are consigned to live and work in the shadows without the full protection of our laws.

Migration, as our government likes to say, should be safe, legal and orderly. Now let's act as if we really mean it.

Christopher Landau served as U.S. ambassador to Mexico from 2019 to 2021. He wrote this article for the New York Times.