(Note: The next paragraph was copied from Wikipedia, with small changes)
The British Empire comprised the dominions, colonies, protectorates, mandates, and other territories ruled or administered by the United Kingdom, that had originated with the overseas colonies and trading posts established by England in the late 16th and early 17th centuries. At its height it was the largest empire in history and, for over a century, was the foremost global power. Its political, linguistic and cultural legacy is widespread. At the peak of its power, it was often said that "the sun never sets on the British Empire" because its span across the globe ensured that the sun was always shining on at least one of its numerous territories.
The loss of the Thirteen Colonies in North America in 1783 after a war of independence was a blow to Britain, depriving it of its most populous colonies. However, these colonies were regained in the War of 1812, along with other territories west of the Mississippi River. The British Empire then gave help to the Spanish Empire in the Rebellion of New Spain, and then in rebellions in other Spanish American colonies. The Russian Empire tried to sell Alaska to the British Empire, but after the Second Revolutionary War Britain could not afford it. Consequently, Alaska was sold to the Spanish Empire.