The whole point of visual meteorological conditions (VMC) is that there is sufficient visibility for a pilot to be able to safely fly by visual reference alone, without reference to instruments. This, by necessity, requires a visibility of at least one to several miles, plus staying a good distance away from any clouds (the exact visibility and cloud-clearance limits depend on the jurisdiction, but all have at least some minimum requirements for these factors); so far, so good.
In many countries, however (including a lot of the big ones, such as the US, Canada, the UK, Australia, France, Germany, and New Zealand), VMC is still VMC even at night, and night VFR flight is perfectly legal (albeit with somewhat greater restrictions on who can fly VFR at night and the qualifications necessary thereto) if the visibility and cloud-clearance requirements are satisfied.1
The underlying assumption is presumably that pilots will still be able to avoid flying into the ground (in either controlled or uncontrolled manner), or each other, by reference to ground lighting and each others' anticollision lights, but this line of reasoning breaks down if you fly over unlighted terrain (of which the countries permitting night VFR flight have quite a lot), especially if it's a moonless night. If it's well and truly nighttime, the moon is either a thin crescent or completely absent from the sky, and the terrain is devoid (or nearly so) of light sources, the ground will be almost completely invisible, with the only hint of its presence being its occlusion of the background stars, and it is difficult to imagine how one would be able to maintain terrain clearance (especially if one's aircraft lacks a radar altimeter). Even worse would be if the stars (and moon, if present) were obscured (by, for instance, high clouds, or smoke from forest fires), in which case one would have no external visual reference at all;2 a non-instrument-rated pilot would find it essentially impossible to maintain control of the aircraft in these circumstances, just as if they were trapped inside a cloudbank during a daytime flight, and even a pilot who is proficient in instrument flight would have difficulty maintaining terrain clearance, especially in mountainous areas (which, inconveniently for our pilot, tend not to be densely populated, and, thus, are rather more likely to be unlighted than flatter terrain).
To eliminate this problem, does the definition of night VMC (in the US or any other jurisdiction) require that the terrain in the area be lighted sufficiently for it to be visible?
1: In many other countries, VFR flight is not permitted at night, and the issue therefore does not arise.
2: Unless you're low enough for your aircraft's lights to illuminate the ground, in which case you're already way in deep shit anyways.