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From within any confluence space you can see the complete page tree by selecting Browse, Pages from the menu at the top of the page, the select View: Tree.
Within the tree it is now possible to simply drag pages from one location to another. You can drag individual pages, or a whole sub-tree of pages in one operation. (It is perhaps advisable to try this on your personal confluence space first, before tackling a larger space. It is easy to accidentally drop pages in the wrong place but once you get used to it moving pages becomes very fast.)