What does it mean to fight a war on two fronts?

According to military terminology, a two-front war occurs, when opposing forces encounter on two geographically separate fronts. The forces of two or more allied parties usually simultaneously engage an opponent in order to increase their chances of success.

Explanation:

the correct answer is the following is a list of inventions made in the medieval islamic world, especially during the "islamic golden age" (8th to 13th centuries),[1][2] as well as the late medieval period, especially in the emirate of granada and the ottoman empire.

science and technology in the islamic world adopted and preserved knowledge and technologies from contemporary and earlier civilizations, including persia, india, china, and greece-roman antiquity, while making a number of improvements and innovations.