The simple answer is that Zane Grey wrote Westerns.
But like all writers he was much more complex than just that. Most of Zane Grey's stories had an overriding moral tone about them, with good morals prevailing over evil.
Another main theme in Grey's novels was that of "change". Characters unwilling to adapt to changing mores, changing technology, or changing customs would often meet with destruction, while those willing to adapt would ultimately succeed.
He also wrote some nonfiction, as well. Being an avid outdoorsman, Zane Grey wrote many nonfictional accounts of his hunting and fishing exploits. While these are highly regarded in some circles, they paled in comparison to his Westerns.
horror books
horrid and calm books
picture books and novels
Mysteries and children's books
she writes children books only
she writes mystery-adventure books
write war book about how people feel
monster
dunnnah
he wrote fairytales
jill tomlinson writes books for kids about animals
Desiderius Eurasmus was a theologian, he wrote books on religion, specificly that of Christianity.