I'll answer the second question.

Hitler's contention (which predated Hitler and was popular throughout the far-right of Germany) was that Germany's surrender in November, 1918 was caused by domestic betrayal at a time when Germany had not yet lost the war.

By November 1918, Germany was in retreat, Austria-Hungary and the Ottoman Empire had both sued for a separate peace, but the German line was still on French soil. The Allies had made it clear that they would not negotiate with a Germany still under Imperial rule (although Kaiser Wilhelm II had been reduced to a figurehead of the military government by this time) and ignored peace overtures in October of 1918.

In a revolutionary crisis on November 7th, 1918, the SPD (Social Democrats) under Friedrich Ebert forced the Chancellor, Prince Max of Baden, to resign and hand over power to the SPD. Two days later, the new SPD government unilaterally declared that the Kaiser and Crown Prince had abdicated and that Germany was now a Republic and sent out feelers for an armistice with the Allies, which was accepted. The government had surrendered while German troops still occupied a significant chunk of France.

Now, Germany was clearly defeated in November of 1918 and fighting on would be prolonging the inevitable, but Erich Ludendorff, the second most important man in the German military by the end of the war, came up with the Stabbed-in-the-back story that socialist revolutionaries had forced German capitulation when they were on the verge of victory as a cover story to shift blame for defeat away from the military. Adolf Hitler's premise that socialist movements were either Jewish or puppets of Jews extrapolated Ludendorff's argument into the idea that the Jews had forced Germany to surrender at its moment of triumph.