What prompted Italy to declare war on Austria-Hungary in April 1915?

Italy, a member of the Triple Alliance with Germany and Austria-Hungary, declared neutrality when World War 1 began in 1914.

This changed, when the Triple Entente, consisting of Britain, France and Russia, offered control of numerous territories to Italy in the Treaty of London to persuade Italy to join forces with them.

In April 1915, Italy joined the Triple Entente by declaring war on Austria-Hungary. Italy suffered great human losses during the war.

After the Central Powers surrendered in1918, Italy struggled to gain what was promised to them in the Treaty of London. They eventually gained partial control over territories promised; many Italians were bitter about this, leading to the rise and success of Benito Mussolini in the coming years.