How come Westeros is so tolerant in terms of religion?

I see it as a matter of power. The Northerners are not Jews, or other prosecuted groups. They also have an incredibly passive religion. They rarely pray, if at all. They have no holidays. Their religious practice can be summed up, in a way, by keep the trees. And the High Sparrow is more philosophical. read more

The Andals did wage religious driven wars against the North, but all were repelled. Over time they kind of just learned to live with one another, and they had thousands of years to do so. Generally most noble houses in Westeros have First Men heritage. read more

The Reach simply doesn’t have the resources to conquer all of Westeros. As others have stated, the Reach does produce the most food as it is the most fertile region, and can field an army that dwarfs the size of most others. It also has the mightiest single fleet in Westeros. Overall, it is the most powerful region. read more