In the 1930s, hotbeds of military danger began to form in the world. Where did they originate?

In the 1930s, hotbeds of military danger began to form in the world. Where did they originate? Why were the Western countries and the League of Nations unable to prevent their emergence and create a system of collective security?

What began to happen in the 30s in the world has passed the attention of Western countries. In fact, the countries of Western Europe and the United States knew very well that Germany was preparing for war, they understood that war was inevitable. But at that time in the world there was already a confrontation between the USSR and the capitalist world. And many countries assumed that Germany would attack the USSR, and they, in turn, would later establish capitalism there. The same opinion was in the USSR itself, because they wanted to use Germany to achieve their political goals.