Britain and the United States were at loggerheads as late as the Civil War (1860-65), and perhaps even shortly thereafter.
They became allies around the turn of the 19th and 20th centuries. This was because of the rise of the Eurasian "Heartland," and of the so-called "Heartland Theories" put forth by people like Britain's HJ MacKinder (in 1904), and his German counterpart, Karl Haushofer.
Early industrialization had given a head start to "Atlantic" powers such as Britain, France, and even the United States, in the nineteenth century race for world power. But by about 1900, countries like Germany and Russia, in what was then the "heartland" of the Eurasian land mass were catching up in industrialization, and they had more people than two of the three aforementioned Atlantic powers by 1900.
At that time, the "heartland" of the "world island" (the Eurasian continent) consisted of 1) modern Russia, 2) modern Eastern European states such as the Baltics, Berlarus, Poland, the Baltics and the Ukraine, and 3) "central Europe," including Germany, Austria, ethnic Germans of the Czech Republic, and possibly Italy (in the Triple Alliance prior to World War I, and the Berlin-Rome Axis of World War II). Note that the last reference to central Europe is my contribution, and not part of the original Mackinder thesis. Despite being vastly different in size, the three components of the "heartland" have similar populations; 140 million Russians, about the same number of Eastern Europeans, and 150 million Germans and Italians.
To use a "modified" form of Mackinder's thesis, whichever power, Germany or Russia, controlled eastern Europe would dominate the combined "heartland." Control of the "heartland" by one or the other (or both in alliance) would lead to the domination of "world island," and control of "world island" could lead to the domination of the world--unless the other "islands" joined forces against them. North and South America were "united" by the Monroe Doctrine, and after 1900, England was eager to cater to the United States. England also made an alliance with Japan in 1902, and had Australia, the last big "island," as a Commonwealth country.
Germany came close to crippling Russia (and capturing Eastern Europe) in World War I, except for the defeat by the Western Allies. Early in World War II, Germany presented the specter of a true "Axis" (according to William L. Shirer in the Rise and Fall of the Third Reich), that would include Germany, Italy, Soviet Russia, and Japan. The object was to divide the lands on the "periphery" of "world Island," with Russia getting a warm water port in modern Iran or Pakistan (and a "corridor" thereto); Germany getting everything west of it, and Japan getting China, India and Southeast Asia to the east. Only Russia upset this plan by demurring; she wanted the Middle East in exchange for letting Germany dominate Europe.