What happened during the time Sonnet 15 was written?

The exact dates when Shakespeare wrote each of his sonnets are not known. But it's safe to assume that this one was written sometime in the 1590s. You can look up the reign of Queen Elizabeth I, who was nearing the end of her life during that decade. But there's no reason to believe that England's internal politics at that time (nor the international politics in which England was involved at that time) are particularly relevant to this poem.