You mean you want the background image to show up too?
It won't. It's a bitmap image. Bitmap images don't show up in Warlight (only vector images do). You either need to convert the entire image (just as you did with the flag), or redraw it with inkscape itself.
The last one is probably better. If it's just about those few lakes and coasts, just draw the shapes and fill them in with a nice blue colour. The same goes for the squares: just draw the square shape in inkscape.
As for text, you need to draw that using the text option in Inkscape. Then, select the text and click ctrl-shift-c (or go path->object to path).
History of Poland Map Development: 2017-09-11 02:08:16