Which three countries caused the league of nations problems?

The League of Nations faced significant challenges from several countries, particularly Germany, Italy, and Japan. Germany was initially excluded from the League and later violated its terms by rearming and pursuing aggressive expansion. Italy's invasion of Ethiopia in 1935 showcased the League's inability to enforce its resolutions, while Japan's withdrawal following its invasion of Manchuria in 1931 further highlighted the League's weaknesses in maintaining peace and order. These actions ultimately undermined the League's credibility and effectiveness.