Answer:
There was a lot of people who were dissatisfied with their reign, especially the supporters of old regime. Additionally, when signing the peace Russia gave up on many territories, which also was seen as a sign of weakness.
Step-by-step explanation:
After the Revolution ended Bolsheviks decided to end the war as they wanted to strengthen their influence in the country.
But, they didn't have enough authority in the country and the Civil War erupted. It was even more deadly than WW1 for the country.