Molotov%E2%80%93Ribbentrop Pact
For Germany, because an autarkic economic approach or an alliance with Britain were impossible, closer relations with the Soviet Union to obtain raw materials became necessary, if not just for economic reasons alone. Moreover, an expected British blockade in the event of war would create massive shortages for Germany in a number of key raw materials. After the Munich agreement, the resulting increase in German military supply needs and Soviet demands for military machinery, talks between the two countries occurred from late 1938 to March 1939. The third Soviet Five Year Plan required new infusions of technology and industrial equipment.[clarification needed] German war planners had estimated serious shortfalls of raw materials if Germany entered a war without Soviet supply.

Q: During conflict, what would prevent transport of materials?
British blockade