The inter-war economic experience, particularly the Great Depression, taught economists and politicians two crucial lessons.

1. The Need for Government Intervention: The first lesson was that an industrial society based on mass production cannot sustain itself if consumption is not also maintained. For this, a stable income and secure employment are necessary, which free markets alone cannot guarantee. Therefore, government intervention in the economy is essential to manage demand, control unemployment, and ensure economic stability.

2. Importance of International Cooperation: The second lesson was about a country's economic links with the outside world. To ensure full employment and global stability, it is vital to manage the international flow of goods, capital, and labour. This requires cooperation and coordination among nations, rather than the economic isolationism that worsened the Depression.