The is to the second social revolution as the steam engine was to the third social revolution

The Plow is to the second social revolution as the steam engine was to the third social revolution.
Plow is an agricultural implement used for cutting, lifting, turning over and partly pulverizing soil. A social revolution is a fundamental change in a society. Alexander Berkman says, Social revolution means the reorganization of the industrial, economic life of the country and consequently also of the entire structure of society.

segregation of schools

Explanation:

ended segregation in public places and banned employment discrimination on the basis of race, color, religion, sex or national origin, is considered one of the crowning legislative achievements of the civil rights movement.