What I’m familiar with is Erica Chenowith who authored work in this area. Here’s her summarizing it on TEDx:

https://www.nonviolent-conflict.org/resource/success-nonviolent-civil-resistance/

Between 1900 and 2006, campaigns of nonviolent resistance were more than twice as effective as their violent counterparts.

https://www.ericachenoweth.com/research/wcrw

https://www.hks.harvard.edu/faculty-research/policy-topics/advocacy-social-movements/paths-resistance-erica-chenoweths-research

One of the reasons is that nonviolent resistance attracts more supporters, and once there’s enough support for enough time, things are more likely to change.

Chenoweth’s painstaking research, unprecedented in its scope and historical breadth, has shed new light on the understanding of civil resistance, political change, and the surprising effectiveness of nonviolent action.

The key ingredients of a successful nonviolent resistance movement, the researchers found, are:

1. A large and diverse population of participants that can be sustained over time.
2. The ability to create loyalty shifts among key regime-supporting groups such as business elites, state media, and—most important—security elites such as the police and the military.
3. A creative and imaginative variation in methods of resistance beyond mass protest.
4. The organizational discipline to face direct repression without having the movement fall apart or opt for violence.

It takes more than months to do anything. The civil rights movement you’re referencing took decades.

Just replied on another comment. Search for Erica Chenoweth https://www.ericachenoweth.com/research/wcrw