这是没主句只有从句的句子吗

But perhaps not for long, as the fascinating city steps onto the world stage.

这句话正不正确? 仿佛没主句，只有从属连词引导的句子。谢谢回答。

But perhaps not for long, as the fascinating city steps onto the world stage.

=But perhaps（it is）not for long as the fascinating city steps onto the world stage.

参考译文：但或许不需要太久这座迷人的/ 使人神魂颠倒的城市就会登上世界舞台。