Though often overlooked in the larger national discussion, Long Island was a battleground of the civil rights movement, according to a new book by local historian Christopher Verga.

Until just several decades ago, black residents were barred from applying to housing in some suburban areas such as Levittown, Verga said in discussing his book, “Civil Rights on Long Island.” School districts were heavily segregated, and the Ku Klux Klan had a large and threatening presence on Long Island.

For most of the Colonial era, Long Island had the largest slave population in the North, he said. Slavery established a racial caste system and a culture of disenfranchisement that was reinforced over decades, through economic policies, housing discrimination, school segregation and more, Verga said at a Sunday lecture at the Bay Shore-Brightwaters Library.

On the eve of Martin Luther King Jr. Day, it’s clear that racial barriers to access on Long Island continue, Verga said.

“According to the Census, we are one of the most segregated suburbs in America,” Verga added. “We haven’t had this conversation, or we don’t feel comfortable having it.”

Nassau County’s population is roughly 75 percent white, 17 percent Hispanic, 13 percent black, and 10 percent Asian, according to the U.S. Census’ 2015 American Community Survey. Suffolk County is 85 percent white, 19 percent Hispanic, 8 percent black and 4 percent Asian.

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Segregation between blacks and whites remains extremely high, and segregation among the Latino, Asian and white populations is increasing, according to a 2015 study by Syosset-based nonprofit advocacy group Erase Racism.

Bay Shore resident Ernie Pontes, 77, said at the discussion that when he grew up, the village was heavily divided by ethnic groups. Today, he said he hopes that we’re a better, more diverse community.