In 1895, the Venezuelan Crisis broke out between Venezuela and Britain over the size of British Guiana. America intervened, invoking the Monroe Doctrine and demanded Britain to submit the boundary disput to arbitration. In OTL, Britain complied and the boundary between Venezuela and British Guiana was settled in 1899.
Main POD: Britain is more ruthless and refuses to follow America's demands. The United States threatens military intervention.
Eventually, Britain declares war on America and Venezuela, beginning the Anglo-American War of 1895.
In OTL, Britain gave in to America's demands because it did not want war. In TTL, Britain is more ruthless and refuses to follow the USA's demands and eventually declares war.
William Hearst is elected Governor of New York in 1906, and goes on to become President two years later.
Later on down the line during World War One, the US is very pro-German, and very anti-British(they are also against the British blockade of Germany). When the RMS Lusitania is sunk, the public blames Britain because "they put American citizens in danger!"
The American people call for war. The USA sees this as the chance to get revenge on the UK, so they use this incident, and the intense British blockade of Germany as reasons to declare war on Britain. The United States of America has joined the Central Powers.