第二次世界大战后国际格局经历了从两极格局到多极化趋势的演变。据此请回答
(1)二战后两极格局确立的原因有哪些?
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(2)促使两极格局向多极化趋势演变的原因有哪些?
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(3)当前国际形势出现和平与动荡并存局面的主要原因是什么?
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