One definition of Northern Mexico includes only the six Mexican states that border the U.S.: Baja California, Chihuahua, Coahuila, Nuevo León, Sonora and Tamaulipas.

From the Gulf of Mexico, it follows the course of the Rio Grande (Río Bravo del Norte) to the border crossing at Ciudad Juárez, Chihuahua, and El Paso, Texas.

Westward from El Paso–Juárez, it crosses vast tracts of the Chihuahuan and Sonoran deserts to the Colorado River Delta and San Diego–Tijuana, before reaching the Pacific Ocean.

[8] According to the International Boundary and Water Commission,[2] the continental border then follows the middle of the Rio Grande—according to the 1848 Treaty of Guadalupe Hidalgo between the two nations, "along the deepest channel" (also known as the thalweg)—a distance of 2,020 km (1,255 mi) to its mouth at the Gulf of Mexico.

The Mexican government encouraged thousands of their own citizens to settle in the region that is now known as Texas and even offered inexpensive land to settlers from the U.S. in exchange for populating the area.

Following the establishment of the current border, several towns sprang up along this boundary, and many of the Mexican citizens were given free land in the northern regions of Mexico in exchange for returning and repopulating the area.

Once viewed as a model of international cooperation, in recent decades the IBWC has been heavily criticized as an institutional anachronism, by-passed by modern social, environmental and political issues.

[4] In particular, jurisdictional issues regarding water rights in the Rio Grande Valley have continued to cause tension between farmers along the border, according to Mexican political scientist Armand Peschard-Sverdrup.

The U.S. Immigration Act of 1917 required the passing of a literacy test and a head tax by Mexicans wanting to enter the U.S. legally; however, during World War I, when labor shortages grew, the provisions were temporarily suspended.

[20] The sudden changes often created bancos (land surrounded by bends in the river that became segregated from either country by a cutoff, often caused by rapid accretion or avulsion of the alluvial channel), especially in the lower Rio Grande Valley.

[27][28][29] On March 27, 2023, at least 38 detained migrants (mostly from Central America) were killed—and dozens more injured—in a fire started in protest inside a locked and crowded detention center cell in northern Mexico, with motives ranging from pending deportation to overcrowding and lack of access to drinking water.

[52] In late 2006, the U.S. Department of Homeland Security (DHS) announced a rule regarding new identification requirements for U.S. citizens and international travelers entering the U.S. implemented on January 23, 2007.

[54][55][56][57] In August 2015, Mexico began enforcing a rule that all foreign citizens that plan to stay in the country for more than seven days or are travelling on business will have to pay a 330 pesos ($21) fee and show their passport.

[63] Horses from Mexico must have a health certificate; pass negative tests for EIA, dourine, glanders, and EP at a USDA import center; and undergo precautionary treatments for external parasites at the port of entry.

The tactic was meant to discourage migration from Mexico into the U.S. by forcing migrants to travel further around barriers where the terrain and weather are more risky, but the strategy was not as successful as initially planned.

Unintentional factors, such as a weakened U.S. economy in the wake of the 2008 financial crisis and the Mexican drug war have made attempting illegal border crossings more risky and less rewarding.

[105] On September 20, 2017, California Attorney General Xavier Becerra filed a lawsuit alleging that the Trump administration has overstepped its powers in expediting construction of a border wall.

[111] Trump signed a proclamation the next day to specify that people crossing the Mexican border illegally would not qualify for asylum; he called the march of migrants from Central America towards the U.S. a "crisis".

[128] On January 17, 2024, a Republican-led non-binding resolution denouncing the Biden-Harris administration's handling of the U.S. southern border passed the House of Representatives by a vote of 225–187, with 211 Republicans and 14 Democrats supporting it.

The humanitarian groups consist of faith-based communities and primarily non-profit organizations that assist deportees, many of whom do not have any resources with them such as money, food, or family information, and who would otherwise become homeless and emotionally and psychologically devastated.

[151] Therefore, the primary purpose of the humanitarian groups on the Mexico side of the border is to create a pathway for transitional support such as providing the deportees food, shelter, clothing, legal help and social services.

[153] Per the La Paz Agreement,[154] the official "border area" extends 100 km (62 mi) "on either side of the inland and maritime boundaries" from the Gulf of Mexico west into the Pacific Ocean.

[155] One "high consequence outcome" was formal removal, which meant the individual would be deemed ineligible for a visa for at least five years and subject to criminal charges if caught re-entering illegally.

The DHS has also worked with the U.S. Department of Justice (DOJ) to increase the number of apprehended individuals crossing the border illegally who are charged with criminal offenses.

For instance CBP officials are not allowed to pull anyone over without a reasonable suspicion of immigration violation or crime, or search vehicles without warrant or probable cause.

According to Brian Segee, a staff attorney with Wildlife Activists says that except high flying birds, animals would not be able to move to other places because of the wall along the border.

In order to prevent Mexican children from illegally coming to America for education, some bordertown schools require official documentation (bills, mail, etc.)

[178] The opposite case was also studied, seeking to find if U.S. students and citizens outsource their medical care from Mexican hospitals; however it was concluded that the use of, "cross-border healthcare diminishes significantly with English language acquisition.

In one study, when repatriated children were asked about how their world perspectives were changed once they returned to Mexico, they spoke to three main areas, "shifting identities, learning and losing named language, and schooling across borders.

"[179] The most frequent point mentioned in terms of changing schooling is the difficulty to adapt to a system in which they are unfamiliar, in a named language they might have lost, and where there is minimal continuity in the methodology of teaching.