Why did BritainFrance and the US not stop fascist aggression in the 1930s?

Britain, France, and the US did not stop fascist aggression in the 1930s primarily due to a policy of appeasement, believing that satisfying the demands of aggressive powers like Nazi Germany would prevent another large-scale war. Economic struggles from the Great Depression also made these nations hesitant to engage in military conflict. Additionally, there was a prevailing isolationist sentiment, particularly in the US, which discouraged intervention in European affairs. This combination of factors allowed fascist regimes to expand unchecked until the outbreak of World War II.