Italy and the United States enjoy friendly relations. The United States has had diplomatic representation in the nation of Italy and its predecessor nations, the Kingdom of Sardinia and then the Kingdom of Italy, since 1840. However, in 1891 the Italian government severed diplomatic relations and briefly contemplated war against the US as a response to the unresolved case of the lynching of eleven Italians in New Orleans, Louisiana, and there was a break in relations from 1941 to 1943, while Italy and the United States were at war.

After World War II, Italy became a strong and active transatlantic partner which, along with the United States, has sought to foster democratic ideals and international cooperation in areas of strife and civil conflict. Toward this end, the Italian government has cooperated with the United States in the formulation of defense, security, and peacekeeping policies. Under longstanding bilateral agreements flowing from NATO membership, Italy hosts important U.S. military forces at Vicenza and Livorno (army); Aviano (air force); and Sigonella, Gaeta, and Naples—home port for the U.S. Navy Sixth Fleet. The United States has about 11,500 military personnel stationed in Italy. Italy hosts the NATO Defense College in Rome.

History 18th, 19th, and early 20th Century Before 1861, no singular Italian nation state existed. The Italian Peninsula was instead divided among several smaller states, each of which the United States established diplomatic relations with. Many of these smaller Italian states were among the first countries in the world to recognize the independence of and maintain diplomatic relations with the United States. For example, the Republic of Genoa officially recognized U.S. independence in 1792 and consular relations were established with the Papal States in 1797. During the Risorgimento, the smaller states inhabiting the Italian Peninsula unified to form the Kingdom of Italy. The United States officially recognized the Kingdom of Italy on April 11, 1861.

During the First Barbary War (1801–1805), the United States was allied with the Kingdom of Sicily against the Barbary corsairs due to a shared interest by both countries in putting an end to the disruption of trade on the Mediterranean Sea caused by the corsairs.

Both Italy and the United States were part of the Eight-Nation Alliance that intervened in the Boxer Rebellion in China from 1899 to 1901.

From the 1880s to 1920, more than 4 million Italians emigrated to the United States and accounted for more than 10 percent of the country's foreign-born population. Italian Americans faced rampant hostility and discrimination. Italian immigration to the United States dramatically declined tapered off in the 1920s largely because of passage of the Immigration Act of 1924.

After the deaths of 11 Italians during a mass lynching in 1891, relations between the nations were strained. The Italian government demanded that the lynch mob be brought to justice and reparations be paid to the dead men's families. When the U.S. declined to prosecute the mob leaders, Italy recalled its ambassador from Washington in protest. The U.S. followed suit, recalling its delegation from Rome. Diplomatic relations remained at an impasse for over a year. When President Benjamin Harrison agreed to pay a $25,000 indemnity to the victims' families, Congress tried unsuccessfully to intervene, accusing him of "unconstitutional executive usurpation of Congressional powers".

The rise of fascism and World War II

The United States and Italy were both members of the Allied Powers during World War I, and President Woodrow Wilson visited Rome while traveling to the Paris Peace Conference. However, at the Conference President Woodrow Wilson opposed Italian irredentist war aims guaranteed in the secret Treaty of London, which ran counter to his 14 Points demanding "open diplomacy" and self-determination. In protest of Wilson and the other Allied leaders' refusal to recognize territorial demands in Yugoslavia and Albania, the Italian delegation under Prime Minister Vittorio Orlando and Foreign Minister Sidney Sonnino walked out of the conference. Wilson tried to mollify the situation by issuing a direct appeal to the Italian people in Le Temps, but it was widely derided by the Italian public.

Since Mussolini's rise to power, the United States applauded him on his early achievements, including helping with relations between the two countries. Relations deteriorated after Italy invaded Ethiopia in 1935.Alexander DeConde, Half bitter, half sweet (1971) p. 222.John P. Diggins, Mussolini and fascism : the view from America (1972) p. 288.

On December 11, 1941, four days after the Japanese attacked Pearl Harbor in December 1941, Germany and Italy declared war on the United States, and the U.S. reciprocated in kind.DeConde, Half bitter, half sweet (1971) p. 245. The U.S. and Britain seized Sicily in 1943 with little combat needed as the Italians pulled out. The Allied invasion of Southern Italy in fall 1943 was a different matter, however, as casualties were high and progress was slow. The Allies captured Rome in June 1944 and very slowly pushed north. The Allies gave much higher priority to the invasion of France in 1944; Italy was a "backwater.".Edwin P. Hoyt, Backwater war: the Allied campaign in Italy, 1943-1945 (Greenwood, 2002).

From 1943 till the end of the war the only part of Italy at war with the United States was the German puppet state the Italian Social Republic. Italian Partisans and Victor Emmanuel III and his loyalists from 1943 overthrew Mussolini and declared war on Germany. Germany quickly overran the entire peninsula. Italy helped the United States and other Allies during the Italian Campaign of World War II.

1946–1989

When the war ended in May 1945, the United States occupied Italy until its plebiscite on the institutional form of the State. The United States helped with the transition from a monarchy to a republic in 1946. Italy had become a valued ally of the United States against the spread of communism in Europe during the Cold War .Mario Del Pero, "The United States and" psychological warfare" in Italy, 1948-1955." Journal of American History 87.4 (2001): 1304-1334.

Italy signed a Peace Treaty with the U.S. and Britain in 1947 and joined the North Atlantic Treaty Organization (NATO) in 1949. The U.S. helped to revive the Italian economy through the Marshall Plan. In the same years, Italy also became a member of the European Coal and Steel Community (ECSC), which eventually transformed into the European Union (EU).

Christian Democrat Prime Minister Alcide De Gasperi (1945–1953) enjoyed considerable support in the US, where he was seen as the man who could oppose the rising tide of Communism – in particular the Italian Communist Party, which was the biggest communist party in a Western European democracy. In January 1947 he visited the US. The chief goals of the trip were to soften the terms of the pending peace treaty with Italy, and to obtain immediate economic assistance. His ten-day tour, engineered by media mogul Henry Luce – the owner of Time Magazine – and his wife Clare Boothe Luce the future ambassador to Rome, was viewed as a media "triumph," prompting positive comments of a wide section of the American press.De Gasperi through American Eyes: Media and Public Opinion, 1945-53, by Steven F. White, in: Italian Politics and Society, No.61 Fall/Winter 2005

During his meetings in the U.S., he managed to secure a financially modest but politically significant US$100 million Eximbank loan to Italy. According to De Gasperi, public opinion would view the loan as a vote of confidence in the Italian Government and strengthen his position versus the Communist Party in the context of the emerging Cold War. The positive results strengthened De Gasperi's reputation in Italy. He also came back with useful information on the incipient change in American foreign policy that would lead to the Cold War and in Italy the break with the Communists and left-wing Socialists and their removal from the government in the May 1947 crisis.The Italian Stabilization of 1947: Domestic and International Factors , by Juan Carlos Martinez Oliva, Institute of European Studies, 2007

Italy faced political instability in the 1970s, which ended in the 1980s. Known as the Years of Lead, this period was characterized by widespread social conflicts and terrorist acts carried out by extra-parliamentary movements. The assassination of the leader of the Christian Democracy (DC), Aldo Moro, led to the end of a "historic compromise" between the DC and the Communist Party (PCI). In the 1980s, for the first time, two governments were managed by a republican (Giovanni Spadolini) and a socialist (Bettino Craxi) rather than by a member of DC.

Many aspects of the Years of Lead are still shrouded in mystery and debate about them continues. There were many, especially on the left, who spoke of the existence in those years of a strategy of tension (strategia della tensione). According to this theory, occult and foreign forces were involved in creating a "strategy of tension". Identified organizations included: Gladio, a NATO secret anti-communist structure; the P2 masonic lodge, discovered in 1981 following the arrest of its leader Licio Gelli; neo-fascist "black terrorism" organizations such as Ordine Nuovo or Avanguardia Nazionale; Italian secret service; and the United States. This theory re-emerged in the 1990s, following Prime Minister Giulio Andreotti's recognition of the existence of Gladio before the Parliamentary assembly on 24 October 1990. Juridical investigations into the Piazza Fontana bombing and the Bologna massacre and several parliamentary reports pointed towards such a deliberate strategy of tension. Milan prosecutor Guido Salvini indicted a U.S. Navy officer, David Carrett, for his role in the Piazza Fontana bombing. He also surprised Carlo Rocchi, a CIA operative in Italy, in 1995 while searching for information concerning the case in the mid-1990s. In 2000, a Parliamentary Commission report from the then center-left government, concluded that the strategy of tension had been supported by the United States to "stop the PCI, and to a certain degree also the PSI, from reaching executive power in the country". (With links to juridical sentences and Parliamentary Report by the Italian Commission on Terrorism)

In 1985, disagreement over the handling of the Achille Lauro hijacking resulted in a heated diplomatic clash between the Italian and United States governments, as well as between elements of their respective militaries. The diplomatic quarrel, known as the Sigonella crisis, escalated into a confrontation and arm standoff between United States special forces units and the Italian military, primarily the VAM (Vigilanza Aeronautica Militare) and Carabinieri. The diplomatic crisis was soon resolved during a conference between Prime Minister Bettino Craxi and President Ronald Reagan.