The Decembrists failed at their mission (namely to overthrow Nicholas and place Constantine on the throne as tsar) because of poor leadership and a small following. After marching upon Senate Square, the soldiers merely stood there, waiting for orders and additional supporters, both of which never came.
Nicholas handled the uprising swiftly, surrounding Senate Square and eventually opening fire on the crowd, which quickly dissipated. He gathered up the officers involved in the failed revolution and jailed them, sending a clear message to all others who dared to question his legitimacy to the throne.
Most interestingly, Nicholas’s elder brother, Constantine, renounced his claim to the throne in the 1820s, not even five years prior to the tsar’s death. His renunciation, however, was kept secret from the public until after Alexander’s death.
Speculation exists as to why this crucial bit of information was kept from the general public. Was it Alexander’s attempt to quell any potential riots, as the public loved Constantine? Did Alexander plan on announcing Constantine’s renunciation, but just wanted to wait for the right political moment?
Regardless of Alexander’s decision to hide Constantine’s renunciation, the Decembrist Revolution exposed Russia to a glimpse of its future. The Decembrists ideologically opposed the Russian autocracy and sought to establish Western sensibilities within the Russian government. This was the first revolution founded on a dramatic shift of ideas.