Yes, violent religious conflicts, like Northern Ireland, can happen in the United States of America.
In the United States of America, there has only been one Catholic President, and many Protestants still hate Catholics.
Many Protestant Christians in the United States doubt that Catholics are loyal to Jesus Christ and the Holy Bible.
The majority of African-American Christians are Protestant Christians, and there is aggressive anti-Catholic attitude among many African-American communities across the United States of America.
Because many Catholics vote for gay marriage rights and abortion in politics, many Protestants are becoming more and more anti-Catholic in America.
Many Protestants are willing to resort to violence to protect their religion, and this is, in fact, a part of Protestant history for centuries, when deeply religious Protestants resorted to war and military warfare to protect Bible Christianity.
This includes many Protestant Christians in the FBI, CIA, Homeland Security, USMC, US Army, US Navy, US Air Force, and throughout every fabric of American life.