Some job ads of US schools require a "statement on diversity". I am not based in the US, and have never written one before. What should one say in a statement on diversity anyway? Am I supposed to state how I would increase the (ethical, scientific, or with regards to other aspects) diversity of the faculty? Would something like "Since I come from Africa, I would make a big contribution to your diversity since currently all faculty members at your department are white" usually be expected?
This should not be a statement about your personal diversity ("I am from Africa"), but rather a statement about how you can contribute to creating a diverse academic community, and how you can help students from diverse backgrounds succeed at the university. As Noah Snyder rightly points out in the comments, your personal diversity would be an obvious thing to include here with a discussion of how that will help you further the goal of attracting and retaining students from diverse backgrounds. If you have no relevant personal experiences, then this should be a discussion of how you plan to further the university's goal of attracting and retaining students from diverse backgrounds.
UC San Diego, which requires such a statement, maintains a webpage describing what should be included. The entire page can be found here.
A few bullet points from their document:
What is the Purpose of a Contributions to Diversity Statement?
- The purpose of the statement is to identify candidates who have professional skills, experience, and/or willingness to engage in activities that would enhance campus diversity and equity efforts.
Are there any guidelines for writing a statement?
- The Contributions to Diversity Statement should describe your past experience, activities and future plans to advance diversity, equity and inclusion, in alignment with UC San Diego’s mission to reflect the diversity of California and to meet the educational needs and interests of its diverse population. Some faculty candidates may not have substantial past activities. If that is the case, we recommend focusing on future plans in your statement. A more developed and substantial plan is expected for senior candidates.
As candidates may not have particular past experiences, there is also some advice on "planned activities:"
The first step is to gather information on activities you would like to pursue while at UC San Diego and how they might fit into the research area, department, campus, or national context. You may consider but are not restricted to current or ongoing campus activities.
For each proposed activity you include, describe the role you envision having and what you would like to accomplish in the next two to five years. Who would you like to engage in your efforts, and how would you plan to engage them? Be as specific as possible, but realistic in terms of your effort and time commitment.
In addition to the quotes above they have more information, including several example statements, and additional resources. They also have a section on how such statement are considered.
Of course, all of this is specific to UCSD, but I imagine it generalizes to other institutions reasonably well.
I'd like to say something about your specific situation.
It seems to me that your being from Africa gives you a rich experience with diversity, since Africa is so diverse in languages, ethnicities, socio-economic levels, political points of view, and on and on. Diversity brings many challenges, and I'm sure there is a lot you could share about the challenges you've faced or observed and what you have learned about how those challenges can be effectively surmounted.
On the flip side: there is a special tension in the U.S. between African blacks and African American blacks. It might be helpful for you (not just for the statement you need to write) to do some reading and reflecting about this. Here is a good introduction to this tension: http://www.npr.org/2013/06/27/195598496/americanah-author-explains-learning-to-be-black-in-the-u-s
The more a candidate can connect personal experience to political beliefs and pedagogical good intentions, the more effective the statement on diversity will be.