germany occupied the balkans after france had already capitulated and britain was fighting them in north africa. the british didnt have the equipment or the manpower to attack hitlers "fortress europe" alone. as for poland, they were in the unfortunate position of being between germany and russia. if the allies had landed in poland (which in itself would have been very difficult) they undoubtedly would have been easily crushed by the german forces who would have had infinitely better lines of supply. also they would have been in danger of ending up at war with the soviets, which would have been disasterous. the fact is that england and france were not prepared to fight a war and germany was.
overall i agree that appeasment was a dumb move, but not as dumb as the move that led to it, which was the incredibly harsh and unfair treaty of versailles. this is what made germany such an unstable place to begin with and allowed people like hitler to come to power. the appeasers were trying to do something reasonable, which was get rid of the strictures of versailles that were causing all the problems. that this would not work was not readily apparent at the time. it should have worked, i think in a more normal course of events it would have. but by that time hitler was is power and he didnt just want to make things better for germany: he wanted world domination.