How did Germany lose Russia as an ally and how does this affect the German war plans?
Russia happened to have a lot of good tanks (T-34 and KV) – which were perfect antitank weapon. Germans strategy was – use tanks to circle and destroy Russian army piece by piece. When Russians destroyed a lot of Germans tanks – Germans lost their advantage. And since USA and Britain helped Russia – they got (by 1943) much more good weapon then Germany.