religion or nationalism

In my opinion, human history has been driven mainly by two major ideas, religion and nationalism. Save the continuing advancements of technologies, nothing has shaped the world we live in more.   Almost all wars have been started over one of the two ideas, and therefore more people have died for these beliefs than for anything else.  I pose three questions.  Which idea is responsible for more deaths in human history; religion or nationalism?  Which idea is most likely to cause the next major war?  And are people any different because of where they were born, or what god they believe in (if they do)?