Side view

Lush side

Sparse side

could we have a pic or two of a leaf... so we can start with an ID ...

will it fall on anything important???

location.... big city name.. to figure out what kind of weather you have ..

presuming it is harmless ... this thing could stand there.. as is.. for another 50 years or so ...

we may never know what caused it ...

as to the canopy ... its seems like the tree has tried to even itself out... due to the lean ... which makes me speculate.. that whatever happened.. happened 10 or 20 years ago ....

what is your base soil type ... it might help us understand how well it is anchored ...

what is the cement pad next to the tree???

ken

It's an Asian maple, probably Acer palmatum. I wouldn't worry much about the lean. It is not really affecting the growth and it doesn't look like it would fall on anything vital.......and IME, a falling JM is a very rare occurrence anyway.

As to uneven canopy density, there could be various reasons but I see nothing that indicates any disease issue. Might be just due to aspect/sun exposure, wind direction, uneven irrigation..........

Definitely a Japanese maple. In person expert inspection would be best way to acquire any assurances or warnings about its condition.

Get a peek at the north side of a lot of trees, most of them aren't thicker than the south if shade isn't involved. The sun is just usually to the south in the northern hemisphere. Some of the trees with different colored new growth really show that off. That 5% less sunlight a lower branch on the northern end of a tree gets just makes it less competitive. You COULD get in there and really look for some sign of damage on that side or the branches on that side but from St Louis I'm not really alarmed.

For your tree, I think it is one of the decorative maples. SOMETHING happened which set it off that way. As someone said it is trying to correct the weight a bit.