This was the WWI battle between Mexico and the US

In 1917, British codebreakers intercepted a message from the German Foreign Minister bound for the German Legation to Mexico. The infamous message, now known as the Zimmerman Telegram, offered Mexico the territory it "lost" to the United States if they joined the ongoing World War I on the German side should the Americans join with the British. They very nearly did when one border clash almost sparked a full-scale war.

At home, it exacerbated tensions in towns on the American-Mexican border, which were already feeling tense because of Pancho Villa's raids across the border and Gen. John J. Pershing's "Punitive Expedition" into Mexico.

One border town, in particular, was feeling the tension. Nogales, which straddles the border in the U.S. state of Arizona and the Mexican state of Sonora, was a town where anyone could cross into either country by simply walking across the street – International Street.

In 1918, the U.S. Army's Intelligence Division began receiving reports of "strange Mexicans" explaining military tactics and movements to the Federal Mexican garrison stationed in and around Nogales. After the publishing of the Zimmerman Telegram, these reports warranted seriously attention.

Even some of Pancho Villa's former troops, who were disgusted by men they called Germans, addressed crowds and agitated the Mexican populace against the United States. The Army began to suspect German influence was at work and moved elements of the 10th Cavalry – the Buffalo Soldiers – into Nogales.

The tension boiled over on Aug. 27, 1918, when a Mexican carpenter was trying to cross the border. He ignored U.S. customs officials who ordered the man to stop (because he was listening to Mexican customs officials ordering him to continue).

Shots were fired by the Americans. The Mexicans returned fire. The Battle of Ambos Nogales had begun.

Between two and five Mexican customs officers and an Army private were killed (the carpenter was not) as citizens in Mexico ran to their homes to grab their weapons and ammo. Meanwhile, the Buffalo Soldiers arrived and captured the hills overlooking the city. Mexican snipers also began to take shots in the streets of American Nogales.

Mexican troops began to dig trenches as American troops began to move house-to-house. By this time, the American soldiers were taking heavy fire from the Mexicans, both regular troops and citizens. So, American citizens took to their homes – and their guns – to take firing positions near the border. The U.S. 35th Infantry even fired a machine gun into the Mexican positions.

Suddenly, a lone figure walked among the bodies of Mexicans and U.S. troops in the street, waving a white handkerchief tied to a cane, the mayor of Mexican Nogales tried to de-escalate the situation by pleading with his citizens to put down their arms. He was shot from the Arizona side of the border.

It wouldn't be until 7:45 that day, after just over three hours of fighting, that the Mexicans waved a white flag from their customs house. American buglers sounded "Cease Fire" and order was, eventually, restored.

In order to prevent such violence from happening again, the town constructed the first-ever border fence between Mexico and the United States.