Would this be a good thesis for an expository essay? "People’s attitude toward animal rights changed in the Renaissance, the 19th century, and the 20th century by becoming more considerate towards animals that were powerless in the past before humans."

Hmmm. Assault rifle sales ("sporting weapons") were 2 million last year in the US. I wonder if these sporting rifles are more considerate towards animals...

Your thesis: I think you could work with it, however, it is very difficult to prove or argue with words such as "attitude" and "more considerate" and "powerless" . I am also wondering where you will get any facts from the 19th century.
A final thought: are animals in the slaughter house "powerless", and just exactly how "considerate" are humans being to them, as compared to 100 years ago? In your arguments, you will have to consider animals for food

Yes, the thesis you provided can be a good starting point for an expository essay about people's changing attitudes towards animal rights throughout history. However, in order to make your thesis more effective, you might want to consider making it clearer and more specific. Here's a revised version of your thesis statement:

"The Renaissance, the 19th century, and the 20th century marked significant shifts in people's attitudes towards animal rights, as growing awareness and empathy led to increased consideration for animals historically marginalized and subjugated by humans."

To support this thesis in your essay, you can follow these steps:

1. Research the Renaissance period and identify specific examples or events that illustrate changing attitudes towards animals. Look for historical figures, art, literature, or philosophical movements that influenced society's perception of animals.

2. Similarly, explore the 19th century and investigate significant developments related to animal rights. Consider influential figures, like Henry Salt or the formation of animal welfare organizations, as well as any societal changes that affected attitudes towards animals.

3. Lastly, examine the 20th century and identify key moments in the advancement of animal rights. Look into animal protection laws, advancements in scientific understanding of animal sentience, and the growth of the animal rights movement.

4. Discuss each period separately, highlighting the specific changes and developments that occurred in people's attitudes towards animals during each time period. Provide evidence, examples, and historical context to support your claims.

5. Throughout your essay, focus on the factors that contributed to the changing attitudes, such as shifts in cultural values, scientific discoveries, influential individuals, or emerging ethical ideologies.

Remember to provide a balanced analysis, acknowledging any lingering attitudes or practices that persisted despite these changes, as well as any societal factors that hindered progress in certain periods.