Since the seventeenth century, the concepts and techniques of calculus have been continuously expanded and widely used to solve various practical problems in astronomy and physics, and great achievements have been made. However, until the nineteenth century, during the development of calculus, the problem of the rigor of its mathematical analysis had not been resolved. In the eighteenth century, many great mathematicians, including Newton and Leibniz, were aware of this problem and worked hard on it, but they failed to solve it. Throughout the eighteenth century, the foundations of calculus were confused and unclear, and many British mathematicians, perhaps still largely bound by ancient Greek geometry, doubted the entire work of calculus.

　　This problem was not completely solved until the second half of the 19th century by the German mathematician Cauchy . Cauchy's limit existence criterion injected rigor into calculus. This was the creation of limit theory. The creation of limit theory enabled calculus to be based on a rigorous analytical basis, and it also laid the foundation for the development of mathematics in the 20th century.
　　Note: During the period of great development of European mathematics in the Middle Ages (14th to 17th centuries) , mathematical research in China (Ming and Qing Dynasties) was basically in a stagnant state. Therefore, Chinese mathematicians have no connection with calculus.