From wikipedia:

Fitting with her statements that The Handmaid's Tale is a work of speculative fiction, not science fiction, Atwood's novel offers a satirical view of various social, political, and religious trends of the United States in the 1980s. Her motivation for writing the novel was her belief that in the 1980s, the religious right was discussing what they would do with/to women if they took power, including the Moral Majority, the Christian Coalition, and the Ronald Reagan administration.[12][failed verification] Atwood questions what would happen if these trends, and especially "casually held attitudes about women" were taken to their logical end.[13]

The plot intro:

After a staged attack that killed the President of the United States and most of Congress, a radical political group called the "Sons of Jacob" uses theonomic ideology to launch a revolution.[8] The United States Constitution is suspended, newspapers are censored, and what was formerly the United States of America is changed into a military dictatorship known as the Republic of Gilead. The new regime moves quickly to consolidate its power, overtaking all other religious groups, including Christian denominations.

The regime reorganizes society using a peculiar interpretation of some Old Testament ideas, and a new militarized, hierarchical model of social and religious fanaticism among its newly created social classes. One of the most significant changes is the limitation of women's rights. Women become the lowest-ranking class and are not allowed to own money or property, or to read and write. Most significantly, women are deprived of control over their own reproductive functions. Though the regime controls most of the country, there are various rebel groups that are still active.