In 1884, American Red Cross disaster relief work was so successful that the International Red Cross modified its mission from providing war relief only to include peacetime and disaster assistance. In this way, Barton and the American Red Cross were honored with the addition of the "American Amendment" to the Treaty of Geneva.  Many Red Cross programs conducted worldwide today evolved from those introduced under Barton’s leadership of the American Red Cross.

Hubbell's fieldwork included the Texas Famine, 1885; Charleston, SC Earthquake, 1886; Mount Vernon, IL Cyclone, 1888; Florida Yellow Fever Epidemic, 1888; Johnstown, PA Flood, 1889; Russian Famine, 1892; Pomeroy, Iowa cyclone, 1892; Sea Islands, SC Hurricane Relief, 1893-1894; Armenian and Turkish Famine, 1896; Cuban Reconcentrado Relief, 1898; Spanish-American War, 1898; Cuban Civilian Post-war Recovery, 1899; and Butler, PA Typhoid Fever Epidemic, 1903-1904. He represented the American Red Cross at several International Red Cross conferences.

Hubbell's American Red Cross contributions are often overshadowed by Clara Barton. She trusted his abilities and relied on him. When she was unavailable, Hubbell was dispatched, when she was called away, he took charge. As a young man in Iowa, Hubbell learned of Barton's Civil War work. In the mid-1870s, he became a professor of science, and later principal of the Dansville, NY Hygienic Seminary.  He met Barton and committed to assist her in establishing an American Red Cross Society.  

At Barton's request, Hubbell studied medicine to better serve the organization as a trained doctor.  In 1881, Hubbell was attending the University of Michigan when Barton heard about the devastating Michigan forest fires.  She organized the first American Red Cross relief effort and diverted Hubbell from his studies to report to the "burnt district,” noting in her book, The Red Cross in Peace and War "… Hubbell… was on the burnt fields …with instructions to examine… the condition of the people and report their necessities … from actual observation.  These duties were faithfully and judiciously performed…" 

Hubbell returned to medical school but was again called away during the 1882 flooding of the Mississippi and Ohio rivers and the Ohio River floods in Spring 1883.  Barton wrote, "Again our field agent was dispatched and did excellent work.  The entire country was aroused and so liberal were the contributions to the various committees of relief that when Dr. Hubbell retired from the field, having completed the work, he had still unexpended funds in hand.  But they were soon needed.  In less than a month occurred the fearful cyclone of Louisiana and Mississippi…"  Hubbell assisted with cyclone relief in May and returned to Michigan and received his medical degree on June 28, 1883. 

At the request of President McKinley, Barton traveled to Cuba. She noted that Cubans had been devastated by “adverse circumstances, racial differences, the inevitable results of a struggle for freedom, the fate of war, and the terrible features of a system of subjugation.”

The American Red Cross arrived in Havana on February 9, 1898, and distributed food, clothing, and medical supplies to the public and hospitals, established orphanages, and organized quarters. On February 15, 1898, the American battleship and the U.S.S. Maine exploded in the Havana harbor, killing 266 of the 354 crew members. The Red Cross cared for survivors.  McKinley called for the withdrawal of American citizens from Cuba. The U.S. Navy Board of Inquiry blamed the explosion on a Spanish mine.  America declared war on Spain on April 25, 1898 and entered into the conflict for Cuba's independence.  The American Red Cross was ready. When Barton arrived in Florida with supplies and food, Red Cross passage to Cuba was barred by the U.S. Navy blockade. Barton proceeded as per the Treaty of Geneva and the Red Cross mission.  

The War Department was poorly equipped to handle the wounded and prisoners of war in U.S. custody.  The American Red Cross was well supplied and staffed but hindered by American military authorities. U.S. Surgeon General Sternberg and others did not want women present during warfare. Initially they refused to allow female nurses on the field. Although Barton and her immediate staff were able to work with the wounded, others were often prevented from working in American-controlled areas.  Barton directed aid to where it was welcomed.  If American doctors refused Red Cross assistance, she attended to wounded Spanish forces.  The Treaty of Paris of December 10, 1898 ended the war. The American Red Cross assisted with postwar recovery efforts, established several hospitals and orphanages. Due to Barton’s influences, the citizens of Cuba also established a Cuban Red Cross. 

The American Red Cross arrived in Johnstown soon after the dam collapse. Barton directed the establishment of shelters; distribution of clothing, food, and medical supplies; and organized local relief committees. The Red Cross constructed a warehouse, three shelters, and an infirmary complex, as well as assisted with the city's rebuilding efforts.  After five months, at the close of the Red Cross operations, these buildings were dismantled.  Some lumber was sent to Washington, D.C. where Barton intended to build the Red Cross Headquarters. The rebuilding of Johnstown lasted five years.

Johnstown recovery efforts increased awareness of the American Red Cross' contributions and capabilities. Barton wrote in Red Cross in Peace and War, “Without a safe, and with a dry goods box for a desk, we conducted financial affairs in money and material to the extent of nearly half a million dollars. The record on our books showed that over twenty-five thousand persons had been directly served by us. They had received our help independently and without begging. No child has learned to beg at the doors of the Red Cross.”

The New York World was a leading newspaper of the times and they were promoting their own fund raising campaign on behalf of the victims of the Galveston Hurricane. They indicated they would turn over the funds that came into their campaign to Miss Barton is she would led the relief in Texas. The American Red Cross arrived on September 15th and took over the Central Texas Relief Committee’s distribution of food, clothing and shelter. Barton established a women’s Red Cross Society to expand services and an African American auxiliary to ensure a fair sharing of relief supplies.

The American Red Cross raised over $120,000 in cash and goods for relief work. Barton’s presence in Galveston increased donations.  J.R. Kemper, a city father, later estimated that more than a quarter of the donations were “due to the appeal of Miss Barton.” The Red Cross made an unusual contribution to the region’s economic recovery by distributing 1-1/2 million strawberry [one and a half million] plants to local farmers. Within six months, there was a good crop of strawberries for harvest. This generated work and money towards the economic recovery of the community. 

Theodore Roosevelt, despite receiving American Red Cross assistance for the Rough Riders during the Spanish-American War, later wrote that he was, “by no means favorably impressed by the type of work she did during the Spanish-American War.”  As the honorary Board of Advisors chairman, he sided with Boardman and later requested withdrawal from the Board of Advisors for his Cabinet members and for himself. Barton responded, “For twenty years this Red Cross work, so small at first – a mere spark has grown up under our hands until its welcome blaze lighted the footsteps of relief for an entire and direful contest of nations, and of which none better than your honored self know the hardships or the needs.” Roosevelt withdrew his support of Barton’s presidency.  This, combined with growing publicity about the internal power dispute threatened to erode public support, caused Barton to lament, This, combined with growing publicity about the internal power dispute, threatened to erode public support. Barton lamented, “The government which I thought I loved, and loyally tried to serve, has shut every door in my face and stared at me insultingly through the windows.”

On May 14, 1904, she resigned.  In 1905, she organized The National First Aid Association of America and became its honorary president.