The middle kingdom got began when Nebhepetre Mentuhotep ll reunited Upper and Lower Egypt
Stalin wanted governments who were loyal and friendly to the Soviet Union, to act as a buffer zone against potential future German aggression. It was agreed Poland would be reorganized under a communist provisional government and free elections would be held at a later date.
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Islam spread so quickly largely in part because its leaders conquered it's surrounding territories... because its lands were well governed and orderly. And most likely the largest reason, trade trade and trade. Hope this helps.