The NSDAP was the largest party in Germany by the time Hitler came to power, backed by a powerful private army of hardened street fighters. In the 1933 election, they accounted for 33% of votes cast. This may not seem like much, but consider that the Weimar Republic was composed of many competing parties, and the two leftmost parties split the vote, with the Social Democrats receiving approximately 20% of the vote and the Communists 17%. The German right had basically united behind Hitler and the Nazis. Even after he seized dictatorial power, the Social Democrats and Communists were unable to combine to effectively resist, due to political disagreements, the meddling of the Soviet Union (the Communists were forbidden from cooperating with the Social Democrats) and the violent and effective repression instituted by the Nazis. Most of the opposition leaders were imprisoned in concentration camps, forced to flee, or to go into hiding, and prominent members were targeted with quite severe harassment.

As to how they got people to join the army; the German Army was not a volunteer organization. True, there was a hard core of long-service professionals; prior to 1933, this had consisted of 100,000 officers and men. These men, especially the officers, tended to be conservative in outlook, virulently anti-communist, at least somewhat anti-democratic, and hugely in favor of rearmament and the regaining of German lands lost at Versailles. For the most part, they were at the very least sympathetic to the Nazis. From the time conscription was brought back into effect in 1935, able-bodied young men were called up and made to serve two-year terms of duty in the army (das Heer), navy (der Kriegsmarine), or air force (der Luftwaffe), which collectively formed the Wehrmacht. When they had finished their terms of duty, they became reservists, subject to call-up in event of war. These men, along with conscripts brought in from previously protected jobs, or young men just coming of age, formed the vast bulk of the German military throughout WWII.

Further, it would be remiss to state that most Germans were opposed to Hitler at all times. If anything, his popularity rose through the late 1930s and early 1940s. Everyone likes to back a winner, and for a period of five or six years, Hitler's regime floated from stunning success to stunning success. This is one of the key reasons why a serious assassination attempt was not made prior to 1944 - the generals and politicians who might have orchestrated it simply thought there was no popular support for a coup, and if anything, Hitler's death would strengthen the remaining Nazis.