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 .