why did europeans became very interested in North America in the 1920s and lost interest two decades later?

Europeans became interested in North America due to ongoing war and later left America because America had been on the rise to become the leading world power. The Europeans were falling behind as they had an on-going war crisis and later their economy fell apart due to the loses they faced in the war.

Explanation:

America in the 1920's was on the rise to become the superpower. It had a surging economy. the great countries of the europe had faced many loses because of the war.