I don't think that there is a "right answer". I would suspect that, if the book delves into "who" designated the Palestine a Jewish homeland, it would go into the rise of Zionism (probably Theodor Herzl) as a reaction to antisemitism in Europe. However, the root cause lies in the old Colonial view that European nations still held at the end of both WWI and WWII; they felt justified in carving up the rest of the world along arbitrary lines, with absolutely no consideration of the peoples already living there and in denial of global nationalistic movements. Their only considerations were preserving the old ideas of spheres of influence and monopolistic access to raw materials and markets.

Vietnam was another direct result of Colonialism -- France wanted her Indochina colony back at the end of WWII, and the US supported France to keep them from forming strong ties with USSR. When France couldn't hold Indochina as a colony, the US stepped in to prevent Communists from gaining control (that old Domino theory -- once again, a little bit of short-sightedness and bad intelligence goes a long way).