There were several reasons actually. First of all, there was a war before. As it is well known, wars are very expensive. Soldiers needed to be equipped, soldiers need to be paid, etc. Then came the need to pay for heavy costs. Who to tax? For some reason the Colonies were chosen, perhaps as the war was quite literally fought by the colonies.
Answer: Appeasement was the right policy for England because it gave them time to prepare and get there army together. Appeasement allowed them to have peace and no conflict for a while which is a good outcome of appeasement. Lord Halifax even promoted appeasement because it allowed them to prepare for the war which happened within a year.
Explanation: It's understandable that having peace through appeasement would put England in advantage during the war and France could focus on theirselves.
Slavery helped support the rich by tending to the things that made them richer (the plantations).