Pasted fŕom AsciiDoc documentation:
You have a number of stand-alone AsciiDoc documents that you want to process as a single document. Simply processing them with a series of include macros won’t work because the documents contain (level 0) document titles. The solution is to create a top level wrapper document and use the leveloffset attribute to push them all down one level.
Why not simply start the wrapper document with a title using an adornment that is not used
in the included files? All other section levels will move down by one automatically.
It this does not help, consider using Sphinx for merging documents. It is specially built for this purpose and offers much more customization options in this regard.