I want to merge the shapefile of Nigeria and Cameroon admin level 1. I downloaded the files from gadm but I cannot merge the files with QGIS or find a shapefile of Africa having countries at states level. Could anybody help me with this?
Simply copy and paste the features from one layer to the other. The second one must be in edit mode for that. Just as you would do with a text editor.
Or take the whole world shapefile from Natural Earth, select the two and export the selection to another file.