句中的 his empire at an end 是由“名词+介词短语”构成的独立主格结构，在句子中用作状语（表示结果）。又如：

He was waiting, his eyes on her back. 他在等着，眼睛望着她的背影。

The old lady was seated in her chair at the window, a rug over her knees. 这位老妇人坐在靠窗的椅子上，膝上盖着一块小毛毯。

The police officer had him up against the wall, both arms behind his back. 警官要他靠墙而立，双手放在背后。