Who until World War 1 was the world's leading economic power was?

Until WWI the world's leading economic power was Great Britain. Her position was maintained through her empire and the world's largest and most powerful navy of the day. The United States was practising a policy of isolation and was not interested in foreign wars and at that time had little or no colonial interests. Other colonial powers at the time were France, Holland, Portugal and Germany but even combined they could not compare to the industrial, economic or military might of the British Empire. As a result of the war Great Britain was economically and militarily weakened and her colonies began campaigning and fighting for independence. This was a slow process that in some cases dragged on until the 1950s and beyond. The result of the decline of the Great Britain and her Empire as an economic power led to led to power vacuums both economically and militarily. These vacuums were filled by the USA and (at least for the period between the two world wars) Germany and Japan.