Hitler's generals were terrified of any major conflict with Czechoslovakia because of the capability and size of the Czech military and warned Hitler that the German military was not in any state to take on that country. The Czechs had been building up their military for two decades at that point. They had a very professional and capable general staff, ability for rapid mobilization, first-rate equipment (very good tanks, artillery, firearms, etc...) and a sizable force that was roughly comparable to Germany's when comparing to the German forces with actual capability, and mountainous terrain with lots of fortifications, whereas Germany was still in the building up process. The Czechs had the best arms factories in the world at the time as well, and the addition of the country to Hitler's empire helped greatly increase its strength.
Hitler himself later admitted, "When after Munich, we were in a position to examine Czechoslovak military strength from within, what we saw of it greatly disturbed us; we had run a serious danger. The plan prepared by the Czech generals was formidable. I now understand why my generals urged restraint.”
In addition, had Hitler attacked, Britain and France might well have attacked as well and German would almost certainly have been defeated.
I was responding to Mirage's post about what the Germans faced in conquering Europe and peoples standing up to aggressors.