During world war i, relations between the united states and mexico were characterized mainly by

Friends and family wave goodbye to Mexicans who are being expelled back to Mexico as the United States begins a national repatriation program. New York Daily News Archive/Getty Images

Economic collapse pushes tens of thousands of farmers in the U.S. Midwest to migrate to California in search of work, and Americans begin to view Mexican workers as competitors for jobs and a drain on social services. This prompts federal authorities to begin a repatriation program for Mexicans and Mexican-Americans, including some U.S. citizens, that forcibly relocates more than four hundred thousand people from Arizona, California, and Texas to Mexico. Wary of the political climate, hundreds of thousands more return to Mexico voluntarily.

Thousands of Mexicans rally in Mexico City after President Lazaro Cardenas signs an order nationalizing all foreign oil companies that operate in the country on March 18, 1938. Petroleos Mexicanos/MCT/Tribune News Service/Getty Images

Rising economic nationalism in the wake of the Mexican Revolution causes U.S. oil companies to fear their investments in Mexico could be expropriated. The 1923 Bucareli Treaty, in which Mexico agreed to respect the rights of oil companies in exchange for U.S. recognition of the sitting Mexican government, sought to settle the issue, but in 1938, Mexican President Lazaro Cardenas reverses that position and nationalizes the oil industry. The United States accepts the move to keep Mexico aligned with the Allied powers during World War II, though it presses for compensation; in 1944, Mexico agrees to pay U.S. oil companies $24 million plus interest.

U.S. President Harry S. Truman is declared a guest of honor during a meeting with Mexican President Miguel Aleman in Mexico City on March 3, 1947. Harry S. Truman Library and Museum

Harry S. Truman becomes the first U.S. president to visit Mexico City. Later that year, the United States, Mexico, and twenty other Western Hemisphere countries sign the Inter-American Treaty of Reciprocal Assistance, or the Rio Treaty. It codifies the “hemispheric defense doctrine,” the principle that an attack against one country will be considered an attack against all countries. The Rio Treaty is invoked several times during the Cold War, including during the 1962 Cuban Missile Crisis, and the United States cites it following the 9/11 terrorist attacks. In 2002, Mexico becomes the first country to formally withdraw from the treaty, which it does in protest over U.S. plans to invade Iraq.

Mexican workers produce steering wheels at Delphi Delco Electronics, a maquiladora plant that builds parts for General Motors. Robert Daemmrich Photography Inc/Corbis/Getty Images

The end of the Bracero temporary worker program [PDF] in 1964 prompts hundreds of thousands of migrant workers to return to Mexico. In response to the resulting demand for jobs, in 1965, the Mexican government establishes an industrial development program [PDF] focused on the U.S.-Mexico border. So-called maquiladoras, or “assembly plants,” are built to employ lower-paid Mexican laborers who will assemble goods for the U.S. market using raw materials sourced from the United States. Maquiladoras quickly become magnets for job seekers living further south; by 1992, the plants employ roughly half a million people and export goods worth $19 billion, or about 40 percent of Mexico’s total exports. The “Mexican Miracle” [PDF], the result of this state-directed economic plan, produces sustained annual economic growth of 3–4 percent for nearly three decades.

U.S. President Nixon's 'Operation Intercept' led to gigantic traffic jams at the U.S.-Mexico border. AP images

In September 1969, U.S. President Richard Nixon declares a global war on drugs, and the United States deploys thousands of agents along the U.S.-Mexico border to execute an aggressive search-and-seizure counternarcotics operation. The action disrupts cross-border trade, and Mexico’s displeasure over not being consulted on the operation leads to a bilateral cooperation agreement between the countries. The U.S. Drug Enforcement Administration (DEA), created in 1973, becomes the primary point of counternarcotics cooperation. However, the 1985 assassination of a DEA agent in Mexico and growing frustration over Mexican authorities’ involvement in the drug trade lead Washington to favor an increasingly unilateral counternarcotics strategy.

Despite the 1976 discovery of massive oil reserves in the Gulf of Mexico, the 1980s see the Mexican economy struggle with rising inflation, widespread unemployment, and unsustainable public debt [PDF]. Mexico defaults in 1982, sparking a regional debt crisis and leading Washington to step in to negotiate debt reduction in exchange for economic reforms. Many economists blame Mexico’s protectionist policies for its economic stagnation, and in 1986, the country takes the first steps toward reducing its trade barriers by joining the General Agreement on Tariffs and Trade (GATT), the precursor to the World Trade Organization (WTO). Two years later, Carlos Salinas de Gortari is elected president on a reform platform. Salinas pushes to further deregulate the economy, paving the way for the North American Free Trade Agreement (NAFTA) between the United States, Canada, and Mexico.

January 1, 1994

U.S. President Bill Clinton signs the North American Free Trade Agreement (NAFTA) into law on December 8, 1993. Mike Theiler/Reuters

NAFTA goes into effect, beginning the fifteen-year process of eliminating tariffs between the U.S., Canadian, and Mexican economies. The deal creates the world’s second-largest trading bloc, after the European Union, and opens the door to expanded diplomatic cooperation between the United States and Mexico on issues including military training, environmental degradation at the border, central bank cooperation, and rule of law. The agreement proves controversial: U.S. labor groups and many Mexican farmers oppose it, and some critics later blame [PDF] the trade liberalization measures for U.S. job losses and increased illegal migration from Mexico. Still, most economists conclude that the deal boosted overall economic growth, including by more than tripling North American trade, and helped transform Mexico’s economy. 

December 1994

A Mexican worker changes a sign showing the exchange rate of the U.S. dollar to the Mexican peso in December 1994. Jose Luis Magana/AP Images

Ernesto Zedillo Ponce de Leon, of the Institutional Revolutionary Party (PRI), is elected president and immediately faces a banking crisis when the value of the Mexican peso plunges in international markets. After U.S. President Bill Clinton fails to get congressional approval for the Mexican Stabilization Act, which would have provided Mexico a $50 billion bailout, fears that a Mexican default could shake the U.S. economy help him obtain a $20 billion loan from the Treasury Department to help Mexico stabilize its currency. Mexico reenters the international capital market by January 1997, but its economic woes continue after low oil prices and the 1997 Asian financial crisis lead to lower-than-expected growth.

A Mexican soldier carries blocks of cocaine seized in drug raids to an incinerator in Tamaulipas, Mexico. Gerado Magallon/Reuters

President Clinton becomes the first U.S. leader to visit Mexico since 1979. He promises Mexican President Zedillo that he will avoid mass deportations of undocumented immigrants and commits to a joint strategy for combating drug trafficking. The plan centers on stopping the flow of drugs into the United States, including by tracking illegal firearms, negotiating new extradition agreements, and allowing DEA agents to be armed while on Mexican soil. Critics worry that the increased cooperation will compromise Mexican sovereignty. By the late 1990s, the United States represents less than 5 percent of the world’s population but consumes roughly half of all drugs globally.

Mexican presidential candidate Vicente Fox talks to his supporters during a rally in Jalapa, Mexico, in 2000. Henry Romero/Reuters

After seven decades of uninterrupted power, the PRI is ousted when Vicente Fox, a member of the opposition National Action Party (PAN), is elected president. Fox takes office vowing to expand trade relations with the United States, reduce corruption and drug trafficking, and boost wages and economic growth. Meanwhile, U.S. President George W. Bush takes office in January 2001 and calls Mexico the most important U.S. foreign policy priority. However, U.S. attention wanes after the September 11, 2001, terrorist attacks and subsequent war on terrorism define U.S. foreign policy for the next two decades.

Felipe Calderon, the presidential candidate representing the conservative National Action Party, hosts his final campaign rally in Mexico City in June 2006. Jorge Silva/Reuters

Presidential candidate Felipe Calderon, a member of the conservative, pro-business PAN party, wins the July election by less than one percentage point over left-wing populist candidate Andres Manuel Lopez Obrador, also known as AMLO. A limited recount confirms the result, but Lopez Obrador claims fraud and mobilizes his supporters to stage mass protests, leading to a protracted legitimacy crisis that threatens to extend beyond Calderon’s chaotic December inauguration. Calderon’s support for expanded trade, immigration reform, and economic liberalization offers Washington a chance to bolster relations on multiple fronts. President Bush, under pressure from his own party, signs legislation in October to authorize seven hundred miles of new border fencing, which the Mexican government opposes.

A Mexican marine stands in front of a burning pile of cocaine at a naval base in Sinaloa, Mexico, in January 2007. Daniel Aguilar/Reuters

The U.S. government says Mexican drug traffickers pose the biggest organized crime threat to the United States and backs an escalation of the drug war launched by Calderon. The Mexican president deploys thousands of federal troops throughout the country to fight cartels and other organized crime groups and establishes a new federal police force. In 2008, the United States and Mexico begin implementing the Merida Initiative, a counternarcotics cooperation framework that provides Mexico roughly $400 million a year in assistance, including military aircraft, surveillance software, and airport inspection equipment. Meanwhile, drug-related killings soar; in 2009 alone, more than 9,600 people are killed in connection with organized crime.