"Same ethnicity" refers to people who belong to the same cultural or racial group. They share common origins, customs, traditions, and sometimes language. Full definition
Places of worship pop up in communities of like people (same ethnicity, culture, faith etc.), so it's no surprise that we see all black churches in predominately black communities, synagogues in predominately Jewish communities, etc.. (religion.blogs.cnn.com)
Grant said historically the concept of a spoiler campaign has meant two candidates of the same ethnicity, often African American, split the demographic during an election, allowing another candidate to win. (nystateofpolitics.com)