Editor’s Note: In 1917, the Wisconsin National Guard transformed into the 32nd Division and made history in the trenches of Europe during World War I. A year earlier, the Wisconsin National Guard gained invaluable experience serving along the Mexican border — the first federal activation since the Spanish-American War — at a time when tensions were high between the two nations. Next year, the Wisconsin National Guard will launch a historical series chronicling the 32nd Division’s formation, training and deployment to Europe.

National Guard units from states across the nation — including Wisconsin — were called to defend the southern border as an international incident threatened to erupt 100 years ago. And in doing so, the National Guard not only validated its new role as the operational reserve of the U.S. Army, but it honed valuable skills for a greater conflict in Europe.

The concerns in 1916 were not the same as those facing the U.S.-Mexican border today. Rather, insurrectionist violence threatened the nation’s southern border — a region already victimized by cross-border bandit raids. These border threats were loosely aligned with post-revolution Mexico’s various splintered political factions.

While Francisco “Pancho” Villa’s deadly raid of Columbus, New Mexico on March 8-9, 1916 sparked a punitive military expedition by the active Army and ultimately required the National Guard to patrol the Mexican border, political unrest between Mexico and the United States had simmered for years. U.S. concerns for its southern neighbor escalated in the fall of 1910 when a popular uprising ended the 30-year rule of President Porfirio Diaz. His successor was assassinated in 1913 and replaced by Victoriano Huerta, a general who had served under Diaz. Huerta’s authority was challenged by Venustiano Carranza, Emiliano Zapata, and Villa.

Meanwhile, the National Guard was facing its own battle for legitimacy. The Militia Acts of 1903 and 1908 and the National Defense Act of 1916 transformed the state militias into a federally trained and funded National Guard. However, simultaneous national calls for universal military service and a proposal for a “continental army” of full-time Soldiers who would assume the National Guard’s traditional homeland response role threatened the continued existence of the National Guard. The pressing need to protect border states from continued Mexican hostilities required an existing military force, and the National Guard made the most of its opportunity to demonstrate its value to the nation.

As the Mexican civil war continued, the U.S. lifted its arms embargo against Huerta’s antagonists, and did not recognize Huerta’s government as legitimate. In 1914, President Woodrow Wilson threw his support behind Carranza, but that relationship was strained when the U.S. occupied the port, and then the city, of Veracruz in response to a report of German weapons delivered to Huerta. Carranza and Zapata denounced the occupation as a violation of Mexican sovereignty. Villa, alone, backed the U.S. action.

After Huerta was defeated and forced into exile, U.S. forces withdrew from Veracruz in November 1914. However, Zapata and Villa turned on Carranza in a fight for control of Mexico, and the fighting often spilled across the border. Active Army troops were unable to secure the 900-mile border. In early 1915, Texas law enforcement uncovered “The Plan of San Diego” — documents calling for Mexicans and Mexican-Americans to reclaim territory lost after the Mexican-American War, and for other ethnic groups to join in the insurrection and kill white American men age 16 and older. Some outlaws who adhered to this plan raided southern Texas towns. As 1915 drew to a close, the U.S. and six Latin American countries officially recognized Carranza as the legitimate leader of Mexico.

This diplomatic action diminished Villa’s claim to power, and the revolutionary leader looked to change the political dynamics by retaliating against U.S. interests, thereby challenging Carranza’s legitimacy. These actions would culminate in Villa’s 1916 attack on Columbus, New Mexico that killed 18 Americans.

Some citizens demanded the U.S. take action to punish Villa, while others wanted to avoid another war with Mexico. Meanwhile, Europe was ablaze as World War I continued into its third year, and President Wilson knew that it was only a matter of time before the United States was drawn into the conflict.

In the years after the Mexican-American War, Mexican and Native American bandits frequently raided U.S. communities across the border, which was difficult to defend. Pursuing the raiders back into Mexico typically had proven more effective than guarding the expansive, open border, but pursuit also strained relations with the Mexican government and its people. Regardless, Wilson decided on a punitive expedition, led by Brig. Gen. John “Black Jack” Pershing, into Mexico to hunt down Villa. Wilson believed such an effort could be accomplished relatively quickly.

However, the expedition’s supply and communication lines into Mexico proved a vulnerability, and also drew resources away from border security. Hostility from Mexican locals and Carranza supporters threatened to divert the expedition from its original mission to hunt down Pancho Villa. Wilson called up 4,500 National Guard troops from Texas, Arizona and New Mexico, and Carranza prepared for war, telling his military commanders in northern Mexico to engage any U.S. troops crossing the border.

Meanwhile, Plan of San Diego raiders attacked Glen Springs and Boquillas, Texas, on May 6, 1916. Some in Carranza’s military were suspected of supporting these raids.

Wilson called up the National Guard in response to this volatile environment.

“The mobilization was the outcome of a national emergency demanding extra military service beyond that which could be furnished by the regular Army,” Brig. Gen. William A. Mann, the Militia Bureau chief, wrote in a 1916 report on the mobilization effort. “The regular Army on the Mexican border could be [reinforced] no other way.”

Gov. Emanuel Philip received a War Department telegram June 18, 1916 citing “the possibility of further aggression upon the territory of the United States from Mexico and the necessity for the proper protection of that frontier” in announcing the activation of three infantry regiments, one cavalry troop, one field artillery battery and one field hospital. The approximately 4,000 Wisconsin National Guard troops mustered at Camp Williams June 22, and took an oath of federal service June 30. The majority of Wisconsin troops departed for Camp Wilson, near San Antonio, Texas, the following day — the field hospital followed a few days later.

By the end of June, 60,000 National Guard troops were serving along the border, and by the end of July that number rose to about 112,000. They found themselves charged with guarding the border from the Pacific Ocean to the Gulf of Mexico.

But the Guard mobilized with the expectation of hostilities, underscored by their subsequent training along the border. Upon arrival, National Guard troops spent nearly a month marching in full gear in the summer heat, often to and from firing ranges, where they would encamp for days. The First Illinois Regiment suffered extensive heat casualties during a 25-mile march in late July, which appeared to motivate other units to persevere.

“Longer and faster hikes were taken by all three Wisconsin regiments today,” the Milwaukee Journal reported. “The poor showing of the Illinois troops in their first day’s hike Monday, July 24th, has aroused the Wisconsin officers and enlisted men to greater effort.” The marches continued and grew in length, and one Wisconsin officer declared his men “hard as rocks” after three months on border duty. By the end of September, Wisconsin National Guard Soldiers joined fellow Guardsmen from Illinois, Missouri, Kansas and Texas on a 15-day, 166-mile march from San Antonio to New Braunfels, Texas — a journey that saw the weather change from extreme heat to hurricane conditions.

“The march also demonstrates how skillfully these civilians were transposed into an army of fighting men after a preparation of only two and a half months,” Col. Moses Thisted of the Third Wisconsin wrote. “Another outstanding feature of this great march was the splendid manner in which the supply trains have been kept moving day and night.”

The National Guard built camps along the border, guarded towns and infrastructure, improved fortifications and manned listening posts along the Rio Grande. They also engaged in mock battles to hone tactics. One such engagement had 14,000 troops march against New Braunfels with 4,000 troops in defense. When the exercise was over, troops had expended more than 80,000 rounds of blank ammunition in what the Milwaukee Journal described as a “magnificent spectacle.”

The National Guard’s presence and activity brought further Mexican raids to a stop, and appeared to influence Carranza as well.

“The National Guard was Wilson’s last resort for averting war with Mexico,” Maj. Brent Orr, of the North Carolina National Guard, wrote in a 2011 monograph for the Army War College. “Within days, Carranza changed his position and used his influence to impact cessation of the Plan of San Diego raids.”

Carranza allowed the punitive expedition to continue, with some limitations, and his military began an aggressive campaign against Villa — finally defeating Villa’s forces in January 1917 at Jimenez. The U.S. punitive expedition left Mexico by Feb. 5.

National Guard units had begun returning to their home states in the fall of 1916 — Wisconsin’s Battery A, 1st Field Artillery and Troop A, 1st Cavalry returned to the state in October. The 3rd Infantry Regiment followed on Dec. 14. The Wisconsin National Guard’s field hospital and 1st Infantry returned in January, the 2nd Infantry in February, and Troop B, 1st Cavalry — which replaced Troop A in October — returned to Wisconsin in early March.

The War Department recognized the National Guard’s service in a Dec. 20, 1916 letter to the Wisconsin National Guard.

“When the National Guard was called into the service of the federal government, the lives of men, women and children along the frontier were in grave danger, owing to the formidable bandit raid from the Mexican side of the boundary,” Secretary of War Newton Baker wrote. “It is not too much to say that had these raids continued, there was danger of international war. From the time of the arrival of the units of the National Guard on the border, the raids ceased and the tension between the two countries began to relax.”

Months of border service not only provided vital training and mobilization experience to National Guard troops, it identified and addressed shortcomings in the federal supply system.

The lessons learned at the border would soon go into use. In January 1917 Germany sought an alliance with Mexico against the United States, and the discovery of the “Zimmerman telegraph” led to the United States declaring war on Germany on April 6, 1917.