Alien History

I don't really know what it is. It looks like a reproduction of an historical painting (or else). but I'm not really sure. I could not find anyone who could help me about this one. Some of the guys look like aliens but I really doubt that it is the case. If anyone know feel free to comment on his one. It was made on top of the 'b to b' stencil. Its size is about 30x20 cm.