What made Germany invasions of Europe difficult to stop during World War 2?

Germany's invasions of Europe during World War II were difficult to stop due to their rapid and coordinated military strategy, known as Blitzkrieg, which combined fast-moving infantry, tanks, and air support to overwhelm opponents quickly. Additionally, the element of surprise and the initial lack of preparedness among many European nations contributed to Germany's early successes. The effective use of Propaganda and psychological warfare also played a role in demoralizing enemy forces, while the extensive network of alliances and treaties allowed Germany to isolate and conquer countries before they could effectively respond.