Former MSNBC contributor Pat Buchanan on Monday insisted that President Barack Obama was trying impose "unnatural and immoral" same sex marriage on the country "by coercion."

The conservative author asserted to Fox News host Megyn Kelly that Obama's support for marriage equality would rally the conservative base, who "are right now riding to the sound of the guns."

"What the president is attempting to do when they say equality of marriage, he's attempting to impose a radical idea onto the entire American people and to do it by coercion," Buchanan opined. "What has been the history? For 2,000 years, all of Western civilization has been engaged in horrendous bigotry because they've denied the right of homosexuals to marry?"

"Well, Pat, there is a history of that in this country," Kelly noted. "We were bigoted and discriminating against blacks for a couple hundred years in this country -- or at least a hundred plus -- and it's not just like because it took us a long time to realize it, it never happened."

"Well, the idea of slavery was evil," Buchanan admitted. "We all agree with that. And the idea of slavery was condoned in a lot of cases in American history and earlier for 2,000 years, but where is the great religious faith which says homosexual marriage is a right of men and women to marry each other? It has not existed in American history and what you're saying then is -- look, is Billy Graham, Pope John Paul II, every pope throughout history, all these moral and religious leaders -- Aquinas, Augustine -- they were all too stupid to recognize the morality of homosexual marriage?"

"It has been universally condemned throughout history," he added. "They believe and I believe that it is unnatural and immoral, the relationship. And we are trying to enshrine that in the Constitution of the United States. Obama hasn't gone that far but that is what they want done."

"And this is the heart of the culture war, Megyn. It is the fundamental beliefs in Christianity, in scripture and tradition, and all those ideas of right and wrong against a new secularist idea which is quite militant, no doubt gaining in strength. That is the root of the culture war. It’s just like abortion. Is it OK? I mean is that a progressive move or is that the killing of an unborn child? These are the things that are really dividing the country and they’re going to continue. I didn’t declare it a culture war, we just admitted it was there."

Think Progress noted that Buchanan was quick to condemn slavery during his Fox News interview on Monday, but after hearing then-Sen. Barack Obama's speech on race in March 2008, the conservative author wondered where the "gratitude" was from black Americans whose ancestors were brought from Africa.

"America has been the best country on earth for black folks," Buchanan wrote in a syndicated column published by several conservative websites. "It was here that 600,000 black people, brought from Africa in slave ships, grew into a community of 40 million, were introduced to Christian salvation, and reached the greatest levels of freedom and prosperity blacks have ever known."

"We hear the grievances. Where is the gratitude?" he asked.

MSNBC announced in February that it had fired Buchanan after a lengthy suspension because his book, “Suicide of a Superpower” -- which included a chapter called, “The End of White America” -- was not fit for public discourse.

Watch this video from Fox News' Happening Now, broadcast May 15, 2012.

(h/t: Media Matters)