FDR claimed that neutrality/isolationism is not a sustainable position for America because he believed that the global geopolitical landscape of the time demanded a more engaged and proactive role for the United States.
During his tenure, although neutrality could have been desirable approach to avoid the entanglements of foreign conflicts, FDR recognized that the rise of aggressive totalitarian regimes like Nazi Germany and Imperial Japan posed a direct threat to democracy and international stability.
FDR understood that the world was becoming increasingly interconnected, and isolationism would not shield the United States from the consequences of global conflicts.
He argued that isolationism could lead to a false sense of security, allowing hostile powers to gain strength unchecked. Instead, he advocated for policies such as the Lend-Lease Act which provided military aid to allies as a way to support countries fighting against tyranny without direct involvement in the war.