Great Britain's industrial revolution greatly strengthened its ability to oppose Napoleonic France. By the end of the Napoleonic Wars in 1815, the United Kingdom was the foremost European power, and its navy ruled the seas.

Peace in Europe allowed the British to focus their interests on more remote parts of the world, and, during this period, the British Empire reached its zenith. British colonial expansion reached its height largely during the reign of Queen Victoria (1837-1901). Queen Victoria's reign witnessed the spread of British technology, commerce, language, and government throughout the British Empire, which, at its greatest extent, encompassed roughly one-fifth to one-quarter of the world's area and population.

British colonies contributed to the United Kingdom's extraordinary economic growth and strengthened its voice in world affairs. Even as the United Kingdom extended its imperial reach overseas, it continued to develop and broaden its democratic institutions at home.

The legislative union of Great Britain and Ireland was completed on January 1, 1801, under the name of the United Kingdom. However, armed struggle for independence continued sporadically into the 20th century.