The deepest integration the United States has with any country, held together by a trade agreement renegotiated under tariff threat, a water treaty from 1944, and the largest flow of remittances on earth — with a border that was itself the outcome of a war.
7 documented events, earliest first. Every card carries its evidence tier and its own sources.
Ended the war the United States had begun in 1846. Mexico ceded roughly half its territory; the United States paid $15 million and assumed claims. The Rio Grande became the Texas border.
Drew the border. Every water, migration and trade instrument since manages a line that was the outcome of a war one side won.
A bilateral agreement under which Mexican agricultural workers came north on short-term contracts, beginning as a wartime labor measure and running twenty-two years. Millions of contracts were issued.
Established the labor relationship as a managed flow rather than an accident, and created the networks that later migration followed after the program ended.
Allocates the Colorado River and the Rio Grande between the two countries: the United States delivers 1.5 million acre-feet of Colorado River water to Mexico each year, and Mexico delivers Rio Grande tributary water to the United States in five-year cycles. Administered by the International Boundary and Water Commission.
1.5 million acre-feet a year from the Colorado to Mexico; Rio Grande deliveries from Mexico measured in five-year cycles.
The one instrument that binds both sides to physical deliveries every year, and the one Mexico has fallen behind on in dry cycles — which is why water, not trade, is the dispute that recurs on a schedule.
The North American Free Trade Agreement among the United States, Mexico and Canada eliminated most tariffs over a schedule and integrated the three economies' supply chains, most visibly in automobiles.
Made the border a production line. Mexico became one of the United States' two largest trading partners, and the integration is the reason later tariff threats carried weight — a partner that cannot leave has to negotiate.
A US security-assistance program for Mexico and Central America against drug trafficking and organized crime — equipment, training and institution-building — enacted in the 2008 supplemental appropriation and running, under successive names, since.
Made drug enforcement a bilateral security program rather than a domestic Mexican matter, with US funds, US equipment and a shared-responsibility framing that both governments have used and disputed.
Renegotiated under threat of US withdrawal from NAFTA and of tariffs, the United States–Mexico–Canada Agreement tightened automotive rules of origin, added labor-enforcement provisions, and set a joint review every six years.
The first time the integration was renegotiated by leverage rather than by consensus, and the six-year review clause makes renegotiation a standing feature rather than a one-time event.
Mexicans abroad, overwhelmingly in the United States, sent home more than $63 billion in 2023 — a record and a larger inflow than Mexico's oil exports or foreign direct investment.
Over $63 billion in 2023, per Banco de México, mostly from the United States.
The labor relationship, measured in money: a flow larger than most bilateral aid programs on earth, running from households rather than governments, and one that any migration policy touches directly.
Standing arrangements rather than events — what the relationship is, as opposed to what happened to it. Where an arrangement runs in one direction, the card says so.
Tariff-free trade in most goods across the three countries, with rules of origin, labor and dispute provisions.
Both directions, and asymmetric: Mexico sends most of its exports to the United States; the United States sends a much smaller share of its exports to Mexico. The party that cannot leave negotiates from that position.
Annual and five-year water deliveries in both directions, administered by the International Boundary and Water Commission.
Both directions and physical. The United States delivers more water than it receives; Mexico's deliveries are the ones that fall behind, and the dispute recurs with the drought cycle.
US funding, equipment and training for Mexican security forces against organized crime, and intelligence sharing.
Runs toward Mexico in money and equipment, and toward the United States in the enforcement it wants done south of the border. The framing of shared responsibility is the point both governments contest.
Nothing is permitted; it happens. Household transfers from the United States to Mexico exceeding $60 billion a year, larger than oil exports.
Runs toward Mexico, and it is the channel that no government controls and every migration policy affects.
Nothing. The deepest integration in the section has no alliance under it. Mexico is not a NATO member, not a Major Non-NATO Ally, and has historically kept US forces off its territory.
The moments the relationship failed. These are on the page deliberately: a relations page that lists only cooperation is advocacy. A rupture is where the real terms become visible.
The United States annexed Texas in 1845, sent troops into disputed territory, and declared war in May 1846 after a clash there. US forces took Mexico City in September 1847. The treaty of February 1848 transferred roughly half of Mexico's territory.
The founding fact of the relationship: it began with one party taking half of the other's land by force. Every asymmetry on this page descends from it, and it is why the page does not describe the two as partners in the way it describes Britain.
The border. The Gadsden Purchase of 1853 adjusted it once more, for money. It has not moved since.
A devaluation in December 1994 became a collapse. After Congress declined to pass a loan guarantee, the Clinton administration assembled a package of up to $20 billion from the Exchange Stabilization Fund and Federal Reserve swap lines, secured against Mexican oil revenues, alongside IMF and other funds.
That the United States would rescue its partner's currency a year into NAFTA, without congressional approval, because the integration had made Mexico's collapse its own problem — and that it would take oil revenue as collateral to do it.
Mexico repaid the US loans early, in January 1997. The episode is the standard reference for what integration obliges the larger party to do.
The United States threatened withdrawal from NAFTA and tariffs on Mexican goods, including a 2019 threat of escalating tariffs tied to migration enforcement. Mexico negotiated; the USMCA resulted.
That the integration built since 1994 could be used as leverage by the larger party, and that the smaller party would concede rather than test the threat — because the dependency the trade agreement created runs one way.
USMCA in force July 2020, with a six-year review that makes the leverage available on a schedule.
Mexico fell behind on its five-year Rio Grande delivery obligations under the 1944 treaty during drought cycles, producing protests by Mexican farmers in 2020 and US pressure that led to delivery commitments in 2025.
That the one instrument requiring physical performance from both sides is the one that fails under stress, and that it fails on a climate schedule neither government controls.
Delivery agreements under pressure; the underlying shortfall recurs with each dry cycle.
What this page has not settled. Published rather than hidden, with what would answer it.
The USMCA renegotiation established that the leverage works. Whether repeated use erodes the integration it depends on — by pushing Mexican policy toward diversification, or by making the six-year review a standing crisis — is a question the next reviews will answer.
The 2026 joint review and what each side does with it.
The treaty allocates flows that drought and upstream use have reduced below the assumptions of 1944. Both governments have negotiated minutes around it rather than reopening it.
A renegotiation, or a delivery failure large enough to force one.
Both governments use the first phrase; critics on both sides use the second. The funding runs one way and the enforcement the other, which is consistent with either reading.
Nothing conclusively; it is a framing dispute. The page reports the instrument and both framings.
Signed February 2, 1848, the treaty ended the Mexican–American War and transferred to the United States what became California, Nevada, Utah, most of Arizona and New Mexico, and parts of four other states. The border every later instrument manages was drawn here, by conquest. The relationship begins with the fact that it was not a relationship between equals, and that has never fully changed.
What is documented: a border drawn by the 1848 treaty; the 1944 Water Treaty that still allocates the Colorado and the Rio Grande, and that Mexico has fallen behind on more than once; the Bracero Program of 1942–1964 that brought Mexican labor north under contract; NAFTA in force January 1, 1994, and its replacement by the USMCA on July 1, 2020, after renegotiation under tariff threat; the 1995 peso crisis and the $20 billion US loan package that stabilized it; the Mérida Initiative of 2008 that made drug enforcement a bilateral security program; and remittances that reached a record $63 billion in 2023, almost all from the United States. The standing structure is integration without alliance — no defense treaty, no mutual obligation beyond trade and water — and the open question is what tariff leverage does to a partner that cannot leave.
This page covers structure, not sentiment. The relationship is asymmetric in every instrument and the page says so in each card rather than in a summary judgment. The 1848 war is the founding rupture and leads the ruptures list for that reason.