The Treaty of Versailles, signed in 1919, ended World War I and imposed severe penalties on Germany, including territorial losses, military restrictions, and significant reparations, which contributed to political instability in the nation. The treaty also established the League of Nations aimed at maintaining peace through collective security, though the USA never joined. While the League had some successes in the 1920s, it ultimately struggled to prevent aggression, exemplified by Japan and Italy's invasions in the 1930s.