BECAUSE THE GREAT WAR DRAINED THEIR SUPPLIES AND MAN POWER! SAME WITH THE THALMOR. unless you and every other stormcloak supporter on these forums have evidence that the Empire had the resources to continue the war, they had no choice but to agree to the "surrender"
Quite the contrary, my friend! The Battle of the Red Ring was won because the Empire had recovered and regrouped while the Thalmor were stretched too thin! Rather than press their advantage and grasp the initiative, the Empire chose to negotiate from a position of strength. Unfortunately, the terms of the armistice favored the Thalmor.