I would agree that most theists are religious (although I think a not inconsiderable number of atheists are also religious outside the US) but not that theism requires it. Theism is just a belief that a god or gods exist. And you don't need a religion for that worldview.Unfortunately theism necessarily organises it self in to religions, which can have both good and bad effects.
This can become large enough to have real power over entire populations. This can and does lead to wars and oppression.
And while I agree that religion has the power to be uniting and dividing, I think that extends to tribalism in general, which very few humans in the world do not internalize. And I think atheists in the US have overfucused on the dangers of religion and been blindsided by bigoted views popping up with no relation to religion but tribalism, nationalism, classism, purity politics, etc. Which is why we're seeing a huge spike in alt right, misogynist, homophobic 'skeptical' atheists.