EXPLAINER: What's behind strained China-Japan relations

TOKYO (AP) — Japan and China on Thursday mark the 50th anniversary of the 1972 normalization of their ties, but there isn't much of a celebratory mood. Improved ties between Asia’s two biggest economies are considered vital to the region's stability and prosperity, but they remain at odds over disputed East China Sea islands and China’s growing military and economic assertiveness in the region.

Here are the key issues in the often strained relations between these powerhouse neighbors:

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