Your basic problem is that most stars are much dimmer than the parts of your scene lit up by artificial lighting. Combined with the diffusing properties of air and all of the particulates and moisture floating around in it, there is a haze from the brighter light reflecting off the stuff in the air and it is drowning out the very dim light from all except the brightest stars or planets.
Since you can't increase the amount of light provided by the stars, your only option to balance the two is to reduce the brightness of the artificial illumination in the scene. Is there a time later at night when the flood lights are turned off and you can shoot the scene while only illuminating the monuments and buildings using techniques such as light painting or controlled flashes. The advantage to either one is that the stars can be exposed for longer while the light you provide for the foreground subjects can be much shorter in duration.
The only other option if you want a darker sky with stars showing in it is to shoot a separate frame for the sky away from the light pollution of the artificial lighting and combine the two shots after the fact. HDR won't really give optimal results in this case because it will pull up the very dim diffused light that is reflected off the moisture, dust, and other particulates in the air along with the stars and that diffused light will continue to limit how many stars are bright enough to shine through the haze.
