the rise of totalitarianism is one of the factor,as the totalitarian countries adopted expansionist policy thus causing threat to other nations, such as Germany’s frequent invasion, England finally declared war on Germany and wwii broke out
Another factor is the Great Depression,where American faced great economy problem and stop sending loans to other nations,it causes the economy situation to break down in Europe especially Germany. She needed a great sum of capital to rebuild her nation but at the time American stopped sending loans and demanded paying the dept,the economy of Germany then totally collasped,leading to the rise of totalitarianism which hostility finally cuased the wwii to broke out
hope it helps!