Germany became increasingly aggressive during 1930s, through 4 important ways, these are as following:
Annexing Austria: With Austria left as a broken remnant, deprived of most of the territories it ruled for centuries and undergoing a severe economic crisis—the idea of unity with Germany seemed attractive also to many citizens of the political Left and Center.
Increasing the size of its military: German rearmament was a policy and practice of rearmament carried out in Germany during the interwar period (1918–1939), in violation of the Treaty of Versailles. It began on a small, secret, and informal basis shortly after the treaty was signed, but it was openly and massively expanded after 1933.
Working to unite with the Sudetenland: The Sudeten and other Germans in Czechoslovakia numbered about 3,000,000 in the interwar period. Because of its German majority, the Sudetenland in the Munich Conference joined Germany.
Introducing the notion of Lebensraum: it was a basic principle of expansion to create a vast German empire for more physical space, a greater population, and new territory to supply food and raw materials.