History , NazismWatch
As a country then the Nazis had very effective and large armed forces that few countries could match.
As a German citizen, then they did manage to inspire a lot of nationalist pride and for those who disagreed, then they were reported and taken in by the Gestapo, imprisoned, sent to labor camps or worse. Yjay inspired a lot of fear.
2. Gestapo - Secret police that snuffed out any opposition. Plus, some people wanted favour from the Gestapo, so they usually reported people who might be in opposition to the regime.
3. Punishments to offenders - Many opposition groups such as the White Rose group (a group of students) were executed using the guillotine (yep) after handing out anti-Nazi leaflets.
4. No other government - Since the Nazi party abolished all other trade unions and political parties (except the NSDAP), overthrowing the Nazis would just create a power vacuum. At the end of the war the soviets and Americans took over Germany for a little while to prevent anarchy.