The Key to Creation brings the Terra Incognita series to a satisfying conclusion. The two warring groups have an experience that is closely modeled after the Arab/Israeli conflict. Or perhaps even the Suni/Shiite division. Each group is descended from a brother. Their relgious histories are similar, however, they bicker over the minor differences. Each side sees the other as heretics. They see similar areas as holy, yet they constantly fight against each other. The devout religious leaders are more concerned with their dogma than the truth. When a religious leader sees evidence that contradicts his religious understanding, he destroys it. The main threads of the story finally connect and wind down in this final novel. The two warring factions have a huge battle with great destruction. Two expeditions both succeed in finding the source of their society. They awake the "father" of the founders of all their religions. He and his fellow beings are worshiped as gods. However, he admits that there are others with more power than him. He uses some of his technology to quickly return to the site of the great battle and help order peace. Both sides reverence him and finally put aside their differences. It is with great difficulty that they do this. They also maintain some of the keys to their respective religious, merging their established iconography, rather than than destroying it. Could this be a possible template for middle eastern peace? (Though it may be difficult to get Abraham to come back to order it.) Endless tit-for-tat revenge seeking will never be appeased.
Two groups of people descended from the same original group. However, they have adopted different customs and religions and absolutely hate each other. Hot heads on both sides continually lead to an escalation of tensions. One guy tries to make his royal fiance happy by massacring people in a religious site. This leads to the other side killing the Queen's brother. Needless to say, the queen is not happy, and leads another attack. This goes on and on. The people have so much animosity that they just can't get along. Religion is very important, but becomes a differentiator rather than a uniter. 
The Edge of the World is a long fantasy book. There are two groups that fight each other. Cities get burned. People sail away. Kids are born. There are competing religions. It was tough to keep interested. The parts that stuck out were the mapmakers. They could commit things to their brain and map the known nautical world. However, one of the characters was also taken in by a fraudster to get a "Fake" map of the world. Most interesting was the note from the author. He has created a "prog rock" album to accompany the book. I'll have to give that a listen.