This period formed the foundation of the modern world:

-American Revolution to World War II

-War of 1812 to World War I

-French Revolution to World War I

-French Revolution to World War II

The period which served as the foundation of the modern world would be from French Revolution to World War II. The amount of things which have changed in this time period was vital for all the changes that have followed ever since.

The correct answer is French Revolution to World War II

Since the beginning of the French revolution, feudalism started failing and the countries became more democratic even though many of them were still monarchies. They started going towards enlightenment and romanticism and modernism and the next time such a monumental historic moment happened that shook the world was world war 2.