What in Shakespeare's background is relevant to Julius Caesar?

Shakespeare lived and worked in a monarchy, his career taking place during the reigns both of Queen Elizabeth I and King James I. They were not titular heads of state; they ruled England while the concept of Divine Right still was accepted by the English people. While they occupied the throne, their power was absolute, since English society viewed it as having been bestowed upon them through their lineage by God. This political structure is relevant to Julius Caesar because it, like all of Shakespeare's plays, was staged at the pleasure of the sitting English monarch, a reality he acknowledged in numerous ways through his plots and characters.

In Julius Caesar, for instance, a sharp distinction is drawn between the commoners and the ruling class. The common people are portrayed as inferior, unthinking creatures, easily swayed and manipulated--in other words, unfit to govern or have a say in government. This portrayal would have seemed reasonable to the ruling class in England, substantiating their own views of society. 

One scene in particular shows Shakespeare's recognition of the English throne. The night before Caesar's murder, Calpurnia is shaken by terrible dreams foreshadowing his death. Furthermore, strange and unnatural occurrences have taken place during the night; graves have given up the dead, a lioness has come into the city to deliver her cubs, ghosts roam the streets shrieking, and "fierce fiery warriors" have fought in the skies over Rome, raining blood down upon the city. When Caesar remonstrates with her that these signs apply to everyone, Calpurnia replies:

When beggars die there are no commets seen;

The heavens themselves blaze forth the death of princes.

Thus does Shakespeare pay tribute to the power of the throne. The death of a ruler is seen as a cataclysmic event, so profound that even nature itself rebels. Furthermore, the assassination of a ruler is most abominable of all for it most horribly disturbs the natural order which, in Shakespeare's world, was founded upon the Divine Right of the English monarch.