Because it’s not just Muslims who are losing their lives at the hands of far-right nationalism.

【说明】网友这个句子不完整，只给了一个原因状语从句，缺少主句。

这个原因从句是个强调句。把it is...who...去掉之后，就好理解了：

Because not just Muslims are losing their lives at the hands of far-right nationalism.

at the hands of far-right nationalism：意为“在极右民族主义的手中”，这是介词短语作“方式状语”，表示失去生命的方式。