I noticed a name and what looks like a number at the bottom left hand corner. Look up the painter's name to see if you can find when and where he did most of his portraits. Google "WWI Medals" and "WWII Medals" and see if you can match any to your portrait. Also Google "Iron Cross" and you will see it was first issued by the Kingdom of Prussia in 1870 (part of the German Empire) and was issued trough WW1. 1939 was when Hitler started issuing them again, with red added to the black and white ribbon of the earlier version; (Black and White were considered Prussian colors) and swastika in the center. So it looks like your man is likely an Prussian/German soldier WWI or before. A library should have a book or two on european uniforms.