Agreed pD. The first opportunity to stop/pause Hitler was the Rhineland in 1936, if the French had set foot in the Rhineland the German troops would of retreated which may have halted Hitler a little - given more voice to those in the government who opposed the action in the Rhineland. With hindsight we can say if the British and French had rearmed at the same rate as the Germans from 1935/6 then there could of been a different result later on. After 1936 the two points that could of justified an invasion are Czechoslovakia (September 1938 and March 1939) and the invasion of Poland rather than standing back and waiting on the border (Poland) or trying to solve it by diplomacy (Czechoslovakia). The French and British could of advanced a long way into Germany whilst the German armed forces were engaged in Poland or Czechoslovakia. The losses could of been high but it would of halted Hitler from completely conquering Poland and given the Poles time to regroup (although when the Soviets invaded from the East - if they still did then that would be the end of Poland as a free state). In the end it depends on the willingness of the French to fight which as was proved in the Fall of France in 1940 that they didn't really want to fight, in which case any invasion of Germany would of been half-hearted and therefore likely to fail.