One of the most obvious similarities between Snow Falling on Cedars and Wild Thorns is of course that both books are about war, but more specifically, both books are about war caused by the desire for territorial domination. Another similarity is that when wars concern territorial domination, they also concern different groups of people, people that often differ both racially and culturally or even ideally; hence, territorial wars, as seen in both books, also lead to prejudices. However, racial prejudices are more clearly discussed in Snow Falling on Cedars.
Snow Falling on Cedars concerns what happened to Japanese-Americans after Japan bombed Pearl Harbor, an event that forced U.S. involvement in World War II. Japan bombed Pearl Harbor because the Japanese Empire wanted total domination over East Asia ("World War II"). They had hoped the attack would prevent the U.S. Pacific Fleet from taking military actions to prevent the Japanese from planned maneuvers in Southeast Asia ("Attack on Pearl Harbor"). One result of Japan's attack is that, just like the Jews were being moved to concentration camps in Europe, the U.S. also moved American-Japanese citizens to concentration camps. Snow Falling on Cedars particularly speaks of the aftermath of the attack on Pearl Harbor with respect to Japanese immigrants settled on the fictional U.S. island of San Piedro in the Straits of Juan de Fuca, just off of Puget Sound near Seattle, Washington. After the attack, the Japanese immigrants on the West Coast were rounded up and sent to the Manzanar concentration camp in California. The novel also particularly speaks of Japanese-American prejudices that remained dominant even after the war, especially focusing a Japanese-American man who was wrongfully accused of murdering a fisherman and eventually acquitted, although 11 out of 12 jury members voted guilty. Hence, in Snow Falling on Cedars, the central theme concerns racial prejudice.
In contrast, while Wild Thorns certainly indirectly deals with prejudices between the Palestinians and the Jews, it more directly concerns animosity between Palestinian nationalists and Palestinian pragmatists during the Israeli occupation of Palestinian territories in the West Bank and Gaza Strip. The two cousin characters Usama and Adil represent the conflicting views of the nationalists and pragmatists respectively. Usama believes that anything and everything should be done to resist the Israelis and create an independent Palestinian nation, while Adil believes that his primary focus should be keeping his family alive and doing what needs to be done to be able to keep providing for his family. The Israeli occupation especially made provision difficult because the Israelis controlled commerce and even taxation, making it very difficult for Palestinians to find work outside of the Israeli job market. Therefore, if someone like Adil became willing to work for the Israeli's just to keep feeding their families, it made them look like traitors to the Palestinian ideal of an independent nation. This conflict between the nationalists and the pragmatists is a theme seen throughout the book, and is especially seen in a conversation between Usama and the bread seller. Usama berates the bread seller for selling Israeli bread, but the seller responds by pointing out the difficulty of being able to survive during Israeli occupation, especially pointing out that even rich men like Usama have gone to work for the Israelis to sustain their income, as we see when the bread seller declares:
Look friend, we're not the first to work with them. While we were still wandering the streets of Nablus looking for bread to eat, your kind were running around Tel Aviv looking for companies to award you franchises so you could sell their products. (68)
Hence, Wild Thorns ultimately contrasts prejudicial feelings between two sides of the same group, the nationalist Palestinians vs. the pragmatic Palestinians, while Snow Falling on Cedars speaks specifically of racial prejudice.