Britain and France had experienced heavy losses and trauma during World War I, and they did not want a repeat of what had happened

 
Latest advances in technology - A breakout of war would result in larger devastation

 
They both had fairly weak economies - War would result in large costs, and they were not able to afford it - concentrated on home issues - poverty, health care and unemployment - Conscription and rearmament would help to lower unemployment

 
They wanted Germany to act as a barrier against Communist Russia

 
It would allow them to strengthen their forces in the meantime, especially their air forces - those extra few years before war broke out gave them the upper hand of having more aircraft than the Germans - remilitarisation of all their forces

 
Failure of the League of Nations meant that Britain and France needed to step up.

 
They were weak, and it allowed them to buy time - became stronger

 
They would have lost the war without appeasement - allowing aggressors to take what they wanted allowed Britain and France to stay out of their way and remain temporary allies - friendlies

 
Role of the public opinion - they did not want to enter a war and they were in 'happy' times, when their country's economy was up and coming, they did not want it to all go to waste in one go.