Thread:Project:Support desk/How to Import Large mediawiki xml Dumps into my existing wiki?/reply

See Manual:Importing XML dumps.

It won't "delete" any existing content. If you have existing pages with the same name, they may be overwritten by generating new revisions in top of the existing ones, although you could go to the history and see the previous content.

Note that what gets imported are page revisions. If the import is older than existing pages, it will generate older revisions of current pages in the history, but the current content of the page will still be shown.