Original: It was the world's first industrialised country and the world's foremost power during the 19th and early 20th centuries, but the economic cost of two world wars and the decline of its empire in the latter half of the 20th century diminished its leading role in global affairs.
Simplified: It was a major world power during the 19th and early 20th century. The economic cost of two world wars and the decline of the British Empire in the latter 20th century reduced its leading role in global affairs.