Germany had a long militaristic, autocratic and authoritarian tradition. Hitler carried this on but the Weimar republic didn't. The Germans failed to develop their democracy to enable it to succeed instead they carried on their strong state led by a powerful leader. The natural even inevitable leader at this time was Hitler. He used the Brown shirts to parade in the streets and is on display to show the militaristic side and he wore uniform when speaking to the people. He used a symbol, the swastika, to signify his party. He based his party on and used propaganda to promote the authoritarian foundations that he intended for Germany. The democracy of the Weimar Republic was built upon weak foundations among the defeat of the First World War so this allows Hitler to reinforce his authoritarian ideas especially since Hitler was against democracy.
Hitler was very politically skilled. He used dualism in the Reichstag to play his opponents off against each other. Despite the Nazis being revolutionary, they came to power using constitutional methods. Hitler would not be satisfied by power that was limited by a constitution and with the presence of other opposing parties. He used clever tactics to eliminate his opponents that culminated in the Reichstag fire in February 1933. This provided apparent crisis for the Nazis but it is now said that van der Lubbe, the Dutch communist really did commit the crime. The Nazis just used this coincidence to their advantage. It apparently showed a 'communist threat' and the Nazi propaganda reflected this threat to ensure that the German people knew about this and would subsequently support Hitler when he arrested the communist deputies leading to the collapse of democracy. The 'Decree for the Protection of the People and State' gave the Government rights to search, arrest and censor whatever they saw necessary to prevent Germany from 'sinking into communist anarchy'. The Enabling Act, only opposed by the SPD, gave full legislative power to Hitler, the Chancellor, for four years. Before the end of the four years, Hitler had done away with the parties and people in a position to enforce the limits on his power. A law was formed called the 'Law against the New formation of parties' stating that all parties except the Nazi party were illegal. Parties such as the Centre party dissolved themselves and allowed Hitler to take control, accepting the Nazi dictatorship.
Another problem for Germany that could have helped overcome Hitler was the fact that the SPD and the KPD wouldn't unite to fight the common enemy. If they had then they could have outvoted Hitler in the Reichstag. At no time in his political career did Hitler and the nazi party have an overall majority in the Reichstag. The Nazis had 43.9% of the votes in the 1933 elections, which wasn't quite a majority. They joined with the Nationalists to obtain 51.8% of the votes, which was only just a majority. Most of the voters didn't actually vote nazi in the elections so despite Hitler having Chancellorship and having power he still didn't manage to gain an overall majority in the Reichstag. In times of crisis people will accept extreme measures such as was Hitler offering, they need to be told what to do especially since they were used to such an authoritarian government rule.
The fact that the German people were so afraid of communism (the 'anti-Communist hysteria') meant that Hitler could exploit this to gain his power. After passing the policy to ban the formation of new parties he managed to 'persuade' the existing parties to disband and threw the SPD and KPD into prison as enemies of the state.
The main reason for Hitler being able to get into power was the First World War because it was linked to lots of other reasons. The First World War laid the foundations of Hitler's ideas and eventually led to a dictatorship in Germany and another World War. The failure of the opposition to unite against him meant that he was able to rise to power quite successfully and easily. The failure of the Republic left the way open for Hitler to come forward and take power successfully as a strong leader was needed to get Germany back on it's feet. The militaristic traditions in Germany was a long-term reason for Hitler being able to gain power as was the Treaty of Versailles and the First World war because they were ultimately the root of the problems Germany was facing that allowed Hitler to gain control and then create a dictatorship. The fear of Communism was quite Long-term but it became stronger through Hitler's propaganda and his hatred of Communists. The democracy of the Weimar Republic had been built on bad foundations after the war and so hadn't got off to a very good start. This allowed Hitler to gain power when it failed as he picked up the pieces afterwards and rebuilt Germany. Hitler's ideas were reinforced when it failed and people were more likely to turn to Nazism because they had seen what had happened when they had tried democracy. Hitler gained power because of the failure of the opposition to go against him and the impact of the First World War on Germany. Germany was weak in many ways at this time and Hitler took advantage in this and was firm in his beliefs, which enabled him to become chancellor.