The U.S. is predominantly Christian, and most of them fall into either the Roman Catholic, Protestant, or Eastern Orthodox churches - Trinitarians, all. In fact, the Trinitarian view of Christian dogma is so ubiquitous in this country, it's easy to forget that there are other interpretations of Christianity, and not just obscure sects.
The Unitarian church is one of the unsung heroes of modern Christianity. In an age where traditional churches are losing members and mass attendance is down, the Unitarian church is growing. It's not one of the big boys as Christian movements go, but its liberal ideology and beliefs that parallel the modern way of life have a way of bringing new members to the flock and erasing disillusionment with antiquated belief systems.
Unitarians are Nontrinitarians, meaning they believe that God is God and that's it. Jesus was a wonderful man and the best moral compass one could hope for, but he was not God, nor was he the Son of God. Unitarians do not believe in the Holy Trinity, in which God, Jesus and the Holy Spirit are seen as three separate facets and beings existing within the same God - to Unitarians, God stands alone.
This belief is what started the movement - Polish Christians who espoused this view were told to change their minds or leave Poland in the 16th century, so they fled to Holland and Transylvania and began calling themselves Unitarians. The church was officially recognized in Transylvania soon after in the Edict of Torda, but remained somewhat underground throughout the rest of Europe.
In England, Unitarianism was somewhat of a myth until the late 18th century, when post-Enlightenment liberation brought on a mad rush of curiosity about freethinking and alternative dogma. From England it spread to Boston by the mid-19th century, and from Boston to the rest of the U.S.
Besides the strict monotheism, Unitarians hold a number of beliefs that set them apart from other Christian movements and offer what some feel is a refreshing take on modern religion. One such belief is that no religion is the "right" one, because nobody can claim to know or profess the "one true path" to God. Essentially, they are saying, "Hey, we might be wrong too - but we're no more wrong than anyone else, and this is what we believe. Join us. Or don't."
Another central tenet is the staunch belief in free will. Man is not inherently evil or "tainted", and life is a series of choices between right and wrong. People are free to make either choice, as mentioned in the Bible.
They don't take the Bible literally though, because they recognize that its authors were humans, and therefore subject to misinterpretation and error. Unitarians fall back on the instinctual knowledge of right versus wrong, regardless of any text.
Room for Rationality
To most people, science and religion are two distinct paths, and never the twain shall meet. In reality, about half of all scientists claim to be religious, and Unitarianism is one of the reasons why - it is one of the Christian movements that actually codifies respect for science and rational thought within the structure of the church itself.
Sure there are scientists who are Catholic and Protestant, but these people either struggle to reconcile their faith with their occupation, or they are very self-delusional. Unitarians welcome critical thinking, even in regards to religion. This open-mindedness is why the church boasts members like Linus Pauling, Ralph Waldo Emerson, Frank Lloyd Wright, Susan B. Anthony, Charles Darwin, Charles Dickens, Florence Nightingale and others. In fact, the church's members include eleven Nobel laureates and seven American presidents.
The dominant Christian churches are the way they are because they began in a time when the church existed to guide, protect and lead the people. The Unitarian church is different because it recognizes that the role of the church has changed - today, religion is more about comfort and spirituality than answers. Sure, there's still guidance, but much of it requires introspection, not commandments from on high.
In fact, the Unitarian church is much closer to the way of living Jesus taught than the religions that supposedly take the Bible as Gospel - this is why the Unitarian church has been called, "A religion of Jesus, not a religion about Jesus."