According to economist Karl Marx and Friedrich Engel’s publication “The Communist Manifesto”, what was the key to ending the struggle between people of upper and lower classes?

Invading armies would isolate the area inside. Restrict any materials from entering or exiting the perimeter until essentially everyone inside the castle would have eaten all the cattle, horses, food. Exhausted all their resources, and are starved out of rebellion, and submit/ surrender to the invading army.