During World War I, the United States actively sold weapons to the Allied powers of Britain and France. In an attempt to limit the role of American-made weapons, Germany threatened to sink any ships crossing the Atlantic with weapons bound for the Allies. Although the Lusitania incident of 1915 got Germany to back away from its policy of unrestricted submarine warfare, its wartime struggles convinced it to re-institute this policy. Knowing that returning to unrestricted submarine warfare would likely draw the US into the war on the side of the Allies, Germany wanted a way to keep the American military occupied elsewhere. With tensions high between the US and Mexico, Germany approached Mexico about an alliance.
Setting the Stage: The Mexican-American War
Tensions have long been high along America’s southern border. In the early days of the Republic, what is now Mexico was the province of New Spain. When Mexico gained independence from Spain in 1821, it bordered the United States along the territory purchased from France in 1803 (the Louisiana Purchase). The United States and Mexico soon clashed diplomatically over the breakaway republic of Texas, which won its independence from Mexico in 1836. Ironically, many Americans had immigrated to Texas illegally, heightening Mexico’s suspicion of the expansion-focused United States.
After multiple attempts, Texas was made part of the United States in 1845. This immediately sparked dispute between the US and Mexico regarding their respective borders: the US claimed the Rio Grande River was the border, while Mexico claimed the Nueces River–further to the northeast–was the border. After a shooting incident in the area between the two rivers, known as the Nueces Strip, launched the Mexican-American War in 1846, Mexico was forced to cede over half of its territory to the victorious United States. After the war, Mexico struggled through many periods of internal unrest following its humiliating loss of territory.
Setting the Stage: Veracruz & Pancho Villa
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Sign up to our Free Weekly NewsletterUnrest in Mexico continued through the early 20th century. Many Mexicans were upset at US foreign interventions in Latin America, which had begun in earnest under President Theodore Roosevelt. They were also tired of political corruption and unrest, especially the Mexican Revolution of 1910, which sparked a rapid chain of leadership changes in Mexico. In 1914, the United States occupied the Mexican port city of Veracruz after the Tampico Incident, where US Navy sailors were arrested while on a mission to protect US property in the region. After Mexican authorities gave what was considered an insufficient apology for the arrest, Congress and US President Woodrow Wilson decided to occupy the city of Veracruz.
Refusal to accept Mexico’s new president, Venustiano Carranza, led revolutionary (and former Carranza ally) Pancho Villa to invade the United States in 1916, likely in direct retaliation for US military assistance to Carranza-allied troops in 1915. On the morning of March 9, 1916, hundreds of raiders led by Villa swarmed the town of Columbus, New Mexico. Eighteen Americans were killed by the time US troops drove Villa’s forces away. In retaliation, the US sent an army into northern Mexico to hunt down Pancho Villa. Its leader, General John J. Pershing, would later be the leader of the American Expeditionary Forces to Europe during World War I.
1915: The Lusitania Incident and Sussex Pledge
As relations between the US and Mexico eroded between 1914 and 1916, tensions also soared between the US and Germany. World War I raged in Europe, but the United States remained neutral. Still, the US had strong economic ties with Britain and France, and this included selling them weapons for the ongoing war. In February 1915, Germany declared that merchant ships bringing weapons to Britain would be targeted by its submarines. On May 7, 1915, the British luxury liner Lusitania was sunk off the coast of Ireland by a German submarine after the passenger vessel had been accused of carrying munitions for Britain.
More than half of the almost 2,000 passengers aboard the Lusitania perished, including 128 Americans. The United States was outraged, and the incident firmly swung public opinion in favor of the Allies. Although Germany had acted within its state rules of engagement, there was tremendous public pressure to refrain from sinking passenger ships. After another passenger ship, the SS Sussex, was attacked in early 1916, American pressure got Germany to sign the Sussex Pledge not to attack passenger vessels.
1917: Unrestricted Submarine Warfare to Return
As the stalemate of World War I continued, Germany was suffering under Britain’s naval blockade. It invested heavily in submarines to fight this blockade and perform a similar, albeit hidden, naval blockade of Britain itself. Germany had a difficult choice: resume unrestricted submarine warfare to try and starve Britain into submission…but risk the United States’ entry into the war on the side of the Allies. Resuming unrestricted submarine warfare would inevitably mean the sinking of American merchant and passenger vessels on the grounds that they were carrying munitions for Britain and France.
In January 1917, the decision was made to resume unrestricted submarine warfare. On January 31, the German ambassador to the United States announced that the policy would go into effect on the following day, February 1. US President Woodrow Wilson was outraged and quickly severed diplomatic relations with Germany. Later that month, after Congress refused to make the proposal law, Wilson armed US merchant ships by executive order. Wilson did not ask for a declaration of war, however, because there was no “smoking gun” of German aggression toward the United States itself.
The Zimmermann Telegram
Unbeknownst to Wilson and Congress, Germany had already made such an aggressive action! On January 17, 1917, British intelligence had intercepted an encrypted telegram from German foreign minister Arthur Zimmermann to Heinrich von Eckhardt, the German ambassador to Mexico. The telegram, named after its sender, anticipated the eruption of hostilities between the US and Germany due to Germany’s resumption of unrestricted submarine warfare. On February 26, just after Wilson had ordered the arming of merchant and passenger ships in the Atlantic, British intelligence shared the decoded telegram with the United States.
The telegram told German diplomats to approach the Mexican government in the event of America’s entry into the war and offer Mexico a military alliance. Explicitly, the military alliance would help Mexico retake the US states of Texas, New Mexico, and Arizona, which had been lost after the Mexican-American War. To assist with this, Germany would offer “generous financial support.” Additionally, Germany wanted Mexico to communicate with Japan and try to get Japan to switch sides in the ongoing war (although Japan played a minimal role due to its location in the Pacific).
The Telegram Revealed: America’s Reaction
On March 1, President Wilson released the Zimmermann Telegram’s text to the public in newspapers. As expected, most Americans were outraged. Some, however, thought the message was a fake due to its lack of feasibility: because of the brutal stalemate on the Western Front, Germany had few resources to spare. Shortly after its publication, Germany acknowledged the telegram, with Zimmermann defending it by declaring that it was only to take effect if America entered World War I.
News of the telegram was inflammatory because it was known that Germany had agents in Mexico. Also, the US still had troops in Mexico pursuing Pancho Villa, making the telegram highly pertinent in that regard as well. Public debate surged, with opinion turning harshly against Germany. Over the course of a month, calls for war increased, and Wilson convened his cabinet on March 20 to discuss the possibility of entering the war. On April 2, 1917, President Woodrow Wilson asked Congress to declare war against Germany.
United States Enters World War I
On April 4, the Senate voted for a declaration of war against Germany, followed by the House of Representatives on April 6. The United States had formally entered World War I. Technically, it was not an Allied power but rather a co-belligerent against Germany. Unlike more recent wars, the United States entered World War I with only a small standing army. Although the US had actively intervened in Latin America, these were not industrialized nations like Germany. Not since the War of 1812 had the United States had to fight an industrialized nation near to, or even greater than, its own strength.
To help the US prepare to fight Germany in Europe, several hundred British and French veterans of trench warfare came to America to train new recruits. On May 18, Congress passed the Selective Service Act to create a draft, or conscription, to fill the US military ranks in preparation for combat. This law is still in effect today, although it has not been used to run a draft since 1973. Eight days later, General John J. Pershing, who had pursued Pancho Villa in Mexico, was named commander of the US forces that would head to France. The American Expeditionary Forces (A.E.F.) would eventually number 4 million men!
Did Mexico Want to Accept the Deal?
Despite high tensions between Mexico and the United States, Mexico was not inclined to accept the deal offered by Germany. Even with German aid, which Mexico figured would be minimal, Mexico’s military was no match for that of the United States, which had dominated Spain in the Spanish-American War twenty years earlier. Ultimately, the offer was formally rejected by Mexico after a commission determined its infeasibility. Japan also firmly denied that it would have accepted any offer to switch sides in the war.
Mexico lacked a domestic arms industry and relied on other nations for weapons, making it ill-equipped to launch any sort of attack on the United States. In terms of industrial capacity, Mexico was also no match for the industrialized United States. The US also had a far greater population than Mexico in 1917, allowing it to overwhelm the Mexicans on any battlefield. Even if Mexico had been able to win sizable chunks of territory in a well-coordinated surprise attack with German-supplied weapons, it certainly could not have kept them against an American counter-offensive.
Post-Zimmermann Relations Between the US & Mexico
In exchange for rejecting the Zimmermann Telegram and remaining neutral, the US agreed to recognize Carranza’s rule in Mexico. After World War I ended, the US had relatively little interaction with Mexico; immigration from Mexico did not become a noteworthy issue until the Great Depression, when the Mexican Repatriation saw angry Americans, often at the state or local level rather than the federal level, force Mexicans (or Mexican-Americans born in the United States) to return to Mexico under threat of violence. During World War II, demand for Mexican labor returned, and the Bracero Program, which lasted for twenty years, saw thousands of guest workers from Mexico labor in American agriculture.
Tensions have periodically resurfaced between the United States and Mexico over post-1960s illegal immigration, drug trafficking, and political unrest in Mexico. Of these, illegal immigration has combined with Mexican drug cartels to create the controversial issue of human trafficking. The governments of the United States and Mexico have clashed regarding how to deal with both immigration and combating drug-related violence. Similar to 1916, some American politicians have argued that the US military should become involved in fighting drug cartels in Mexico to stem the flow of narcotics northward. While this scenario is unlikely to occur, critics say that such rhetoric only harms US-Mexico diplomatic relations.
Implications Today: Role of Military Intelligence
The successful interception and decryption of the Zimmermann Telegram in 1917 was a watershed moment for cryptography and military intelligence. Intercepting enemy signals, known as SIGINT for signals intelligence, is now a major field of espionage and intelligence. Since 1917, both information-sending and information-capturing technology has advanced through many evolutions. The US National Security Agency, or NSA, is the primary intelligence agency for monitoring electronic communications.
Sending and breaking codes famously played a significant role in World War II, where the Allies were able to break the German Enigma codes and Japanese codes. The Americans also used Navajo code-talkers in the Pacific to confound the Japanese, who had no speakers of Navajo, to help break the codes. After World War II, the use of cryptography continued, including during the Korean War. Today, in any conflict, all parties seek to capture and decode their enemies’ transmissions to gain valuable intelligence on capabilities, planned attacks, and potential weaknesses that can be exploited.
