Complex sentence: It was largely devoted to the collection of ceramics and precious objects of medieval art (although also including many items from the Oxus Treasure) most of which became the property of the nation, either by donation in his lifetime or by bequest at his death.
Split into simpler sentences: It was largely devoted to the collection of ceramics and precious objects of medieval art (although also including many items from the Oxus Treasure). Most of them became the property of the nation, either by donation in his lifetime or by bequest at his death.