What brings these revivals to an end?
Secular, real-world concerns catch up to them. World War I was the ending of the third Great Awakening. The Iraq War, global warming, and America's financial problems and concern about its place in the world may bring an end to what may be this fourth awakening. (We're too close to it historically to make an accurate judgment now.)
In what ways has religion been a unifying force in this country? How has it been divisive?
Americans have always seen themselves as a people protected by God. The Puritans thought of themselves as a City on a Hill, with this nation as providential and special. Whatever we did, God was on our side. This belief led to some tragic consequences such as Manifest Destiny, which convinced Americans they could do whatever they wanted with the Indians and Mexicans, for example.
It has also led to a lot of intolerance - in colonial times, intolerance towards Baptists and Quakers. One reason James Madison was so keen on forging the First Amendment was that he had seen persecution of Baptists in Virginia. He had heard about a Baptist bullwhipped by an Episcopal priest on horseback. Later on Catholics and Jews faced the same kind of intolerance.
Fortunately the First Amendment provides protection. It allows any religion to be practiced freely without endorsing any specific religion. It's a work of genius, perhaps the greatest element in the Constitution.
