The Weimar Republic replaced the Imperial German government after the end of World War I. It declined for many different reasons, eventually being replaced by the government of Adolph Hitler and his Third Reich.
Most of the problems were brought on by the crippling economic issues caused by the Great Depression and war reperations. Without a strong economy the Weimar Republic’s leaders could not maintain political stability and soon all sorts of groups were vying for control of the Reichstag. Most notable were the Communist and Nazi parties. High unemployment resulted in a fractured political coalition after the 1930 election making it nearly impossible to garner a legislative majority. The last few Chancellors were forced to rule through decree rather than legislative action, which caused more unrest. Hitler would eventually use this power of decree to take control of the government.
With little real power remaining, von Hindenburg, who has been serving as Reichsprasident, decided that he could control Hitler and his party if he kept them close. This is how Hitler was appointed Chancellor in 1932, which would prove to be a crippling blow to the Weimar. Hitler was able to eventually pass The Enabling Act of 1933, which granted him dictatorial powers in the Reichstag and eventually installed his Third Reich. Most historians agree that the passage of the act was the end of the Weimar Republic.
So it was a combination of both economic and political events that killed the Weimar.