It was only after that people started gathering in large groups and formed more complex institutions

It was only after the Industrial Revolution that people started gathering in large groups and formed more complex institutions.

Explanation:

The Industrial Revolution paved the way for the establishment of large institutions as it became a need with growing possibilities of mass production. A well-managed and organized working in synchronous of large groups of people was made possible as the skills of human resource management developed post the Industrial revolution. The organization of people dispensed improved results and thus, the methods were adopted permanently.

Multiplying frequency by period