Why were large powerful militaries and elite cadres of soldiers essential in the early modern era?

Due to advances in military industry, soldier training, and technique.

Explanation:

During the ancient period and the Middle Ages, mass military operations were launched to achieve specific military objectives. With the development of science, technology, and advances in the military industry, this practice has diminished. With the training of soldiers, with the development of the technique, smaller military units were organized that numbered significantly fewer soldiers to carry out certain military operations. Fewer well-trained soldiers were more comfortable to coordinate. Also, these troops performed individual tasks faster, and sometimes these operations were crucial to achieving a particular strategic advantage on the battlefield.

the answer is a new goverment.