Wallpaper patterns are maddeningly difficult to trace because they are constantly re-used and modified for the next generation, especially traditional images like this. That said, here's 3 things you can check out: 1. how wide are the strips? 2. is it on plaster, or sheetrock?, and 3. are the seams overlapped, or butt-joined? The reason for 1. is that screenprints, which came in about 1940 or so, are generally 27" wide, while earlier paper, in the US, is often 18", and English paper of most eras is usually 20.5"; the reason for 2. is that sheetrock can be a dating tool. Sheetrock panels along the line of 2' x 2' are not unknown in the 1910s and 20s, but full-size panels of 4'x8' really began to take off in the 1930s and 40s and by the 1960s were commonly replacing plaster; the reason for 3. is that wallpaper was still being overlapped in some areas of the US as late as the 1940s, but the butt seam was the norm.

In this case we may be looking at an overlap to the far right (just to the right of the last column of stars). This sort of patriotic motif alternating with a nondescript medallion was common in the 1930s and 40s, but it also could be from the 50s (see above, "maddeningly difficult, etc."). The rainbow effect is interesting. This could be a design feature (as could be the faint wave-like background) but these affects could also be from simple deterioration of the paper, which we can assume to be highly acidic, or maybe the residue from another paper put on top that was stripped away? Good luck with your plans.