Wollstonecraft wrote Vindication only three years after the outbreak of the French Revolution of 1789, which had been inspired by the American Revolution of 1776. Needless to say that revolution was in the air, and all over the world, men were standing up and demanding democratic rights as free and rational beings.
We can get a sense of this environment when Wollstonecraft writes, "Let not men in the pride of power, use the same arguments that tyrannic kings and venal ministers have used, and fallaciously assert that woman ought to be subjected because she has always been so" (3.23).
Wollstonecraft was a genius for many reasons (did you read this book? It's awesome) but one big reason was her ability to take advantage of a huge historical moment. While men were running around saying that any rational person had the right to a democratic voice, it was Wollstonecraft who raised her hand and said, "Uh yeah, that same right should apply to women too." After all, there is really no fair way to acknowledge the equality of all men without acknowledging the equality of women, too. Way to carpe that diem, Wollstonecraft.
So the historical setting for this book is crucial, since Wollstonecraft's arguments would have been much more difficult to make without using the spirit of revolution as a springboard.