What's the meaning of the word in this sentence?
This year marks exactly two countries since the publication of Frankenstein; or, The Modern Prometheus, by Mary Shelley. Even before the invention of the electric light bulb, the author produced a remarkable work of speculative fiction that would foreshadow many ethical questions to be raised by technologies yet to come.
This year marks exactly two countries...... two countries? I don't understand. The followings are two books, aren't they? Why countires?