If Britains peace party had won and pulled out of the war in the summer of 1940 is an interesting question it seems improbable that Germany could have succesfully invaded successfully. What would the long term effects have been if Britain was out of the war the dutch , Belgian and french colonies would have come under the control of the pro fascist or Nazi puppet governments. Without the royal navy to block them they could have supplied Japan with the materials they needed for their China campaign and would probably meaning the Japanese would not have involved the US by attacking Pearl harbour in 1941 without the facing of the US sanctions imposed to punish their attck on china that cut off their supplies of key minerals such a petrol and rubber etc. Japan would have stayed neutral or given its hand would have been free attacked russia and continued the war of 1936 in Manchuria. Potentialy the Turks without the threat of British intervention might have turned to the axis wanting to regain lost territory. This would have given the Germans millions of fresh troops and made their supply lines to the Crimea easily protected sea routes allowing the German armies to be well supplied even at the maximum extent of their advance. The Russian forces used for the counter offensive in the winter of 1941 quite simply these troops would habe been tied down fighting Japan in Manchuria. The Germans could have accessed raw materials from the Belgian colonies for minerals the dutch colonies for rubber and oil and the persian gulf for oil. This could have made the war in the east a diffrent proposition for the Soviets and the idea that the US would go to war for the communists seems a little unlikely. Without the losses sustained from the western allies and with the entire airforce available for use in the east and without the lost production from bombing the picture would have been different. Thank goodness the peace party didn't win and Britain fought on because the potential alternantives are interesting but horrific.