The Teller Amendment is an amendment made by the United States (US) Congress to the country's 1898 declaration of war on Spain. This legislation plays a critical role in US-Cuba relations, and has had long-lasting effects on both of these countries for more than a century. Under the Teller Amendment, the US was forbidden to annex or govern the island of Cuba, and Cuba could not become a US territory.

Throughout the 19th century, Cuban citizens made various attempts to win independence from Spain, which had controlled this island for many years. Due to Cuba's close proximity to the US, the United States watched this struggle very closely. Some people in the US likened the Cuban struggle for independence to the American battle for independence from Great Britain during the 1700s. American businesses were also concerned about the heavy investment in Cuban sugar plantations, and how a fight with Spain could impact this industry.

By the 1890s, Cuba had launched a successful battle against Spain for independence. As a precaution, the US military sent a ship to Havana to ensure the US mainland and the country's business interests wouldn't be threatened. On 15 February 1898, this ship, the U.S.S. Maine, exploded under mysterious circumstances. This spurred the US to declare war on Spain on 11 April 1898. Even today, no one knows what caused the explosion that launched this war.

The Spanish-American war was very brief, and lasted only four months before a treaty was signed. During the war, some people in the US assumed that after the war was won, the Americans would annex Cuba in the same way they had annexed Puerto Rico and other nations. Under the sponsorship of Colorado Senator Henry Teller, Congress passed the Teller Amendment on 19 April 1898. The Teller Amendment states that no matter the outcome of the war, the country cannot annex Cuba.

After the Americans won the war, they withdrew from Cuba as promised, with the exception of a small military base that remained. In 1901, Connecticut Senator Orville Platt introduced the Platt Amendment. The Platt Amendment repealed the Teller Amendment, and allowed the US to maintain a military presence in Cuba indefinitely. In fact, the US maintained a base at Guantanamo Bay for well over a century.

Modern historians often argue that sugar was the inspiration for the Teller Amendment. During the 19th century, Colorado was a major exporter of sugar. Many believe that Teller introduced his amendment in an effort to keep Cuban sugar imports from competing with his state's businesses. By preventing Cuba from becoming a part of the US, Teller was better able to protect Colorado's industry from competition.