The Spanish Civil War had a significant impact on the military strategies and technologies that were later used in World War II. It served as a testing ground for new warfare technologies and tactics. For instance, aerial bombardment, as seen in the bombing of Guernica, showcased the destructive potential of air power, which was extensively used in WWII. The war also saw the use of combined arms tactics, integrating infantry, tanks, and aircraft, a strategy that became a staple in WWII. Additionally, the conflict allowed countries like Nazi Germany and the Soviet Union to test their military capabilities and equipment, which they further developed and deployed during WWII.

The global shift towards extremist ideologies severely undermined the League of Nations. The League, founded on principles of collective security and international cooperation, struggled to respond effectively to the challenges posed by the totalitarian regimes. These regimes, prioritising national interest and expansionist agendas over international cooperation, often flouted the League's principles and decisions. For instance, Japan's invasion of Manchuria and Italy's conquest of Abyssinia challenged the League's authority and exposed its weaknesses. The League's inability to prevent aggression and maintain peace amongst its member states significantly diminished its credibility and effectiveness.

The Great Depression significantly influenced the foreign policies of democracies like Britain and France, primarily leading to a more isolationist and appeasement-oriented stance. Economically weakened and socially strained, these countries were keen to avoid the financial and human costs of another war. Britain and France, therefore, adopted policies of appeasement towards aggressive moves by Germany and Italy, hoping to maintain peace and stability. This approach was evident in their responses to events like the remilitarisation of the Rhineland and the Munich Agreement. Their economic vulnerabilities and desire to focus on domestic issues led them to underplay the threats posed by totalitarian regimes.

Fascism and Communism gained popularity during the Great Depression as they offered radical alternatives to the failing capitalist democracies, which were struggling to address the economic crisis. Fascism, with its emphasis on strong leadership, national pride, and military might, appealed to those disillusioned with the perceived weakness and indecisiveness of democratic governments. It promised rapid industrial growth and national revival. Communism, on the other hand, appealed to the working class and those hardest hit by the Depression, advocating for a classless society and the end of capitalist exploitation. Both ideologies thrived on the widespread discontent and desire for change, presenting themselves as viable solutions to the economic turmoil.

Economic policies played a critical role in the rise of totalitarian regimes in Germany, Italy, and Japan. In Germany, the Nazi regime implemented policies aimed at economic self-sufficiency and rearmament, which temporarily alleviated unemployment and boosted the economy, thus gaining public support. Italy, under Mussolini, pursued corporatism, where the state controlled major industries, aiming to stabilise the economy and reduce class conflict. In Japan, the military government focused on heavy industrialisation and military expansion to address economic challenges. These policies not only consolidated the regimes' power internally but also set the stage for their aggressive foreign policies.