Name major events in World War II contributed to Hitler's success in conquering these territories.
Your question does not specify which territories are at issue. Are you referring to the Sudentland region of Czechoslavakia, or Eastern European parts of the Soviet Union, like Ukraine and Belorus? Without knowing that, I can't provide a good answer. If you can provide additional background information on your question, I can possibly provide a better answer.
I suspect the assignment from which your question derives refers to one or the other, as the Sudentland region was conquered "peacefully" as a result of the Munich agreements, whereas the Soviet Union was the victim of a massive armed invasion involving many German army divisions utilizing the so-called Blitzkrieg strategy. Similarly, Austria was peacefully -- many would say willingly -- annexed by Germany in what was called "the Anschluss," while Poland was the victim of a brutal invasion from one side by Germany and by the other side by the Soviet Union. In other words, "peaceful" annexations prior to the initiation of Operation Barbarossa (the invasion of the Soviet Union) of territories within other countries with large German populations versus armed invasions of countries like Poland and Russia.
During the late 1930s, Hitler accomplished a number of his territorial objectives due to the diplomatice ineptitude of the Western powers, mainly Britain and France. Those territorial gains unified German-speaking populations surrounding Germany with Germany, with minimal use of force. Subsequent invasions of other countries were conducted to accomplish broader objectives, like enslaving the Slavic peoples and exterminating Jewish populations throughout Europe.