Because the empires mentioned in the Bible were usually ruled by a king, the empires themselves are often referred to as "kings," "kingdoms," or both.  - Daniel 8:20-22.
4 Ngenxa yokuthi le mibuso okukhulunywa ngayo eBhayibhelini yayivame ukubuswa yinkosi, le mibuso ngokwayo kuvame ukubhekiselwa kuyo ngokuthi "amakhosi," "imibuso," noma kokubili. - Daniyeli 8:20-22.